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Answers to Selected Exercises

( \newcommand{\kernel}{\mathrm{null}\,}\)

2max(a,b) 2min(a,b) 4max(a,b,c)

4min(a,b,c)

(no); 1 (yes) 3 (no); 3 (no) 7 (yes); 7 (yes)\ 2 (no); 3 (no) 1 (no); 1 (no)

7 (no); 7 (no)

2n/(2n)! 23n/(2n+1)! 2n(2n)!/(n!)2

nn/n!\

no

no

\dstAn=xnn!(lnxnj=11j)

fn(x1,x2,,xn)=2n1max(x1,x2,,xn), gn(x1,x2,,xn)=2n1min(x1,x2,,xn)

[12,1); (,12)[1,); (,0](32,); (0,32]; (,0](32,); (,12][1,) (3,2)(2,3); (,3][2,2][3,); ; (,);; (,3][2,2][3,)

; (,); ; (,); ; (,)

; (,); [1,1]; (,1)(1,); [1,1]; (,)

(0,3] [0,2] (,1)(2,)

(,0](3,)

14 16 6

1

neither; (1,2)(3,); (,1)(2,3); (,1](2,3); (,1][2,3] open; S; (1,2); [1,2] closed; (3,2)(7,8); (,3)(2,7)(8,); (3][2,7][8,)

closed; ; \set(n,n+1)n=integer; (,)

\setxx=1/n, n=1,2,; , S1= rationals, S2= irrationals any set whose supremum is an isolated point of the set , the rationals

S1= rationals, S2= irrationals

Df=[2,1)[3,), Dg=(,3][3,7)(7,), Df±g=Dfg=[3,7)(7,), Df/g=(3,4)(4,7)(7,)

, \setxx(2k+1)π/2 where k=integer \setxx0,1 \setxx0

[1,)

4 12 1 2

2

1117 23 13

2

0,2 0, none 13,13

none, 0

0 0 none 0 none

0

0 0 none none none

0

none

none

none

32 32

12

limxr(x)= if n>m and an/bm>0; = if n>m and an/bm<0; =an/bm if n=m; =0 if n<m. limxr(x)=(1)nmlimxr(x)

limxx0f(x)=limxx0g(x)

lim supxx0(fg)(x)lim supxx0f(x)lim infxx0g(x); lim infxx0(fg)(x)lim infxx0f(x)lim supxx0g(x)

from the right continuous none continuous none continuous

from the left

[0,1), (0,1), [1,2), (1,2), (1,2], [1,2] [0,1), (0,1), (1,)

tanhx is continuous for all x, cothx for all x0

No [1,1], [0,) n=(2nπ,(2n+1)π), (0,) n=(nπ,(n+1)π), (,1)(1,1)(1,)

n=[nπ,(n+12)π], [0,)

(1,1) (,) x0(2k+32π), k= integer x12 x1 x(k+12π), k= integer x(k+12π), k= integer x0

x0

p(c)=q(c) and p(c)=q+(c)

f(k)(x)=n(n1)(nk1)xnk1|x| if 1kn1; f(n)(x)=n! if x>0; f(n)(x)=n! if x<0; f(k)(x)=0 if k>n and x0; f(k)(0) does not exist if kn.

c'=ac-bs, s'=bc+as

c(x)=e^{ax}\cos bx, s(x)=e^{ax}\sin bx

f(x)=-1 if x\le0, f(x)=1 if x>0; then f'(0+)=0, but f_+'(0) does not exist.

continuous from the right

There is no such function (Theorem~2.3.9).

Counterexample: Let x_0=0, f(x)=|x|^{3/2}\sin(1/x) if x\ne0, and f(0)~=0~.

Counterexample: Let x_0=0, f(x)=x/|x| if x\ne0, f(0)=0.

-\infty if \alpha\le0, 0 if \alpha>0

\infty if \alpha>0, -\infty if \alpha\le0

-\infty -\infty if \alpha\le0, 0 if \alpha>0

0

Suppose that g' is continuous at x_0 and f(x)=g(x) if x\le x_0, f(x)=1+g(x) if x>x_0.

1 e

1 e^L

f^{(n+1)}(x_0)/(n+1)!.

Counterexample: Let x_0=0 and f(x)=x|x|.

Let g(x)=1+|x-x_0|, so f(x)=(x-x_0)(1+|x-x_0|).

Let g(x)=1+|x-x_0|, so f(x)=(x-x_0)^2(1+|x-x_0|).

1, 2, 2, 0 0, -\pi, 3\pi/2, -4\pi+\pi^3/2\ -\pi^2/4, -2\pi, -6+\pi^2/4, 4\pi

-2, 5, -16, 65

0, -1, 0, 5

0, 1, 0, 5 -1, 0, 6, -24 \sqrt2, 3\sqrt2, 11\sqrt2, 57\sqrt2 -1, 3, -14, 88 min neither min max min neither min

min

f(x)=e^{-1/x^2} if x\ne0, f(0)=0 (Exercise~)

None if b^2-4c<0; local min at x_1=(-b+\sqrt{b^2-4c})/2 and local max at x_1=(-b-\sqrt{b^2-4c})/2 if b^2-4c>0; if b^2=4c then x=-b/2 is a critical point, but not a local extreme point.

\dst\frac{1}{6}\left(\frac{\pi}{20}\right)^3 \dst\frac{1}{8^3} \dst\frac{\pi^2}{512\sqrt2}

\dst\frac{1}{4(63)^4}

M_3h/3, where M_3=\sup_{|x-c|\le h}|f^{(3)}(c)|\

M_4h^2/12 where M_4=\sup_{|x-c|\le h}|f^{(4)}(c)|

k=-h/2

monotonic functions

Let [a,b]=[0,1] and P=\{0,1\}. Let f(0)=f(1)=\frac{1}{2} and f(x)=x if 0<x<1. Then s(P)=0 and S(P)=1, but neither is a Riemann sum of f over P.

\frac{1}{2}, -\frac{1}{2}

\frac{1}{2}, 1 e^b-e^a 1-\cos b \sin b

f(a)[g_1-g(a)]+f(d)(g_2-g_1)+f(b)[g(b)-g_2]

f(a)[g_1-g(a)]+f(b)[g(b)-g_p]+\sum_{m=1}^{p-1}f(a_m)(g_{m+1}-g_m)

If g\equiv1 and f is arbitrary, then \int_a^b f(x)\,dg(x)=0.

\overline{u}=c=\frac{2}{3} \overline{u}=c=0

\overline{u}=(e-2)/(e-1),\ c=\sqrt{\overline{u}}

n! \frac{1}{2} divergent 1 -1

0

divergent convergent divergent convergent convergent

divergent

p<2 p<1 p>-1 -1<p<2 none none

p<1

p-q<1 p,q<1 -1<p<2q-1 q>-1, p+q>1 p+q>1

q+1<p<3q+1

\deg g-\deg f\ge 2

2 1 0 1/2 \quad 1/2 \quad 1/2 \quad

1/2 \quad

\sqrt A 1 1 1 -\infty

0

If s_n=1 and t_n=-1/n, then (\lim_{n\to\infty}s_n)/(\lim_{n\to\infty}t_n)=1/0=\infty, but \lim_{n\to\infty}s_n/t_n=-\infty.

\infty, 0 \infty, -\infty if |r|>1; 2, -2 if r=-1; 0, 0 if r=1; 1, -1 if |r|<1 \infty, -\infty if r<-1; 0, 0 if |r|<1; \frac{1}{2}, \frac{1}{2} if r=1; \infty,\infty if r>1 \ \infty, \infty

|t|, -|t|

1, -1 2, -2 3, -1

\sqrt{3}/2, -\sqrt{3}/2

If \{s_n\}=\{1,0,1,0, \dots\}, then \lim_{n\to\infty}t_n=\frac{1}{2}

\lim_{m\to\infty}s_{2m}=\infty, \lim_{m\to\infty}s_{2m+1}=-\infty\ \lim_{m\to\infty}s_{4m}=1, \lim_{m\to\infty}s_{4m+2}=-1, \lim_{m\to\infty}s_{2m+1}=0\ \lim_{m\to\infty}s_{2m}=0, \lim_{m\to\infty}s_{4m+1}=1, \lim_{m\to\infty}s_{4m+3}=-1\ \lim_{n\to\infty}s_{n}=0 \lim_{m\to\infty}s_{2m}=\infty, \lim_{m\to\infty}s_{2m+1}=0\

\lim_{m\to\infty}s_{8m}=\lim_{m\to\infty}s_{8m+2}=1, \lim_{m\to\infty}s_{8m+1}=\sqrt2,\ \lim_{m\to\infty}s_{8m+3}=\lim_{m\to\infty}s_{8m+7}=0, \lim_{m\to\infty}s_{8m+5}=-\sqrt2,\ \lim_{m\to\infty}s_{8m+4}=\lim_{m\to\infty}s_{8m+6}=-1

\{1,2,1,2,3,1,2,3,4,1,2,3,4,5, \dots\}

Let \{t_n\} be any convergent sequence and \{s_n\}=\{t_1,1,t_2,2, \dots,t_n,n, \dots\}.

No; consider \sum 1/n

convergent convergent divergent divergent \ convergent convergent divergent

convergent

p>1 p>1

p>1

convergent convergent if 0<r<1, divergent if r\ge1\ divergent convergent divergent

convergent

convergent convergent convergent

convergent

divergent convergent if and only if 0<r<1 or r=1 and p<-1 convergent convergent

convergent

divergent convergent convergent

convergent if \alpha<\beta-1, divergent if \alpha\ge\beta-1

divergent convergent convergent

convergent

\sum(-1)^n \sum(-1)^n/n, \sum\dst\left[\frac{(-1)^n}{ n}+\frac{1}{ n\log n}\right]\ \sum(-1)^n2^n

\sum(-1)^n

conditionally convergent conditionally convergent absolutely convergent

absolutely convergent

%\begin{exercisepatch1}

Let k and s be the degrees of the numerator and denominator, respectively. If |r|=1, the series converges absolutely if and only if s\ge k+2. The series converges conditionally if s=k+1 and r=-1, and diverges in all other cases, where s\ge k+1 and |r|=1.

\sum(-1)^n/\sqrt n 0

2A-a_0

F(x)=0,\ |x|\le1 F(x)=0,\ |x|\le1 \ F(x)=0,\ -1<x\le1 F(x)=\sin x,\ -\infty<x<\infty\ F(x)=1,\ -1<x\le1; F(x)=0,\ |x|>1 F(x)=x,\ -\infty<x<\infty\ F(x)=x^2/2,\ -\infty<x<\infty F(x)=0,\ -\infty<x<\infty\

F(x)=1,\ -\infty<x<\infty

F(x)=0 F(x)=1,\ |x|<1; F(x)=0,\ |x|>1 \

F(x)=\sin x/x

F_n(x)=x^n; S_k=[-k/(k+1),k/(k+1)]

[-1,1] [-r,r]\cup\{1\}\cup\{-1\},\ 0<r<1 [-r,r]\cup\{1\},\ 0<r<1 \ [-r,r],\ r>0 (-\infty,-1/r]\cup[-r,r]\cup[1/r,\infty)\cup\{1\},\ 0<r<1\ [-r,r],\ r>0 [-r,r],\ r>0 (-\infty,-r]\cup[r,\infty)\cup\{0\},\ r>0 \

[-r,r],\ r>0

Let S=(0,1], F_n(x)=\sin(x/n), G_n(x)=1/x^2; then F=0, G=1/x^2, and the convergence is uniform, but \|F_nG_n\|_S=\infty.

3 1 \frac{1}{2}

e-1

compact subsets of (-\frac{1}{2},\infty) [-\frac{1}{2},\infty) closed subsets of \dst\left(\frac{1-\sqrt5}{2},\frac{1+\sqrt5}{2}\right) (-\infty,\infty) [r,\infty),\ r>1

compact subsets of (-\infty,0)\cup(0,\infty)

Let S=(-\infty,\infty), f_n=a_n (constant), where \sum a_n converges conditionally, and g_n=|a_n|.

``absolutely"

means that \sum|f_n(x)| converges pointwise and \sum f_n(x) converges uniformly on S, while

means that \sum|f_n(x)| converges uniformly on S.

\dst{\sum_{n=0}^\infty(-1)^n\frac{x^{2n+1}}{ n!(2n+1)}}

\dst{\sum_{n=0}^\infty(-1)^n\frac{x^{2n+1}}{(2n+1)(2n+1)!}}

1/3e 1 \frac{1}{3} 1

\infty

1 \frac{1}{2} \frac{1}{4} 4 1/e

1

x(1+x)/(1-x)^3 e^{-x^2} \ \dst{\sum_{n=1}^\infty\frac{(-1)^{n-1}}{ n^2} }(x-1)^n;\ R=1

\mbox{Tan}^{-1}x=\dst{\sum_{n=0}^\infty(-1)^n\frac{x^{2n+1}}{(2n+1)}};\ f^{(2n)}(0)=0;\ f^{(2n+1)}(0)=(-1)^2(2n)!;

\dst{\frac{\pi}{6}=\mbox{Tan}^{-1}\frac{1}{\sqrt3}=\sum_{n=0}^\infty \frac{(-1)^n}{(2n+1)3^{n+1/2}}}

\cosh x=\dst{\sum_{n=0}^\infty\frac{x^{2n}}{(2n)!}}, \sinh x=\dst{\sum_{n=0}^\infty\frac{x^{2n+1}}{(2n+1)!}}

(1-x)\sum_{n=0}^\infty x^n=1 converges for all x

\dst{x+x^2+\frac{x^3}{3}-\frac{3x^5}{40}+\cdots} \dst{1-x-\frac{x^2}{2}+\frac{5x^3}{6}+\cdots} \dst{1-\frac{x^2}{2}+\frac{x^4}{24}-\frac{721x^6}{720}+\cdots}

\dst{x^2-\frac{x^3}{2}+\frac{x^4}{6}- \frac{x^5}{6}+\cdots}

\dst{1+x+\frac{2x^2}{3}+\frac{x^3}{3}+\cdots} \dst{1-x-\frac{x^2}{2}+\frac{3x^3}{2}+\cdots} \dst{1+\frac{x^2}{2}+\frac{5x^4}{24}+\frac{61x^6}{720}+\cdots} \dst{1+\frac{x^2}{6}+\frac{7x^4}{360}+\frac{31x^6}{15120} +\cdots}

\dst{2-x^2+\frac{x^4}{12}-\frac{x^6}{360}+\cdots}

\dst{F(x)=\frac{5}{(1-3x)(1+2x)}=\frac{3}{1-3x}+\frac{2}{1+2x}= \sum_{n=0}^\infty[3^{n+1}-(-2)^{n+1}]x^n} 1

(3,0,3,3) (-1,-1,4)

(\frac{1}{6},\frac{11}{12},\frac{23}{24},\frac{5}{36})

\sqrt{15} \sqrt{65}/12 \sqrt{31}

\sqrt3

\sqrt{89} \sqrt{166}/12 3

\sqrt{31}

12 \frac{1}{32}

27

\mathbf{X}=\mathbf{X}_0+t\mathbf{U}\ (-\infty<t<\infty) in all cases.

\dots\mathbf{U} and \mathbf{X}_1-\mathbf{X}_0 are scalar multiples of \mathbf{V}.

\mathbf{X}=(1,-3,4,2)+t(1,3,-5,3)

\mathbf{X}=(3,1,-2,1,4,)+t(-1,-1,1,3,-7)

\mathbf{X}=(1,2,-1)+t(-1,-3,0)

5 2

1/2\sqrt5

\set{(x_1,x_2,x_3,x_4)}{|x_i|\le3\ (i=1,2,3) \mbox{ with at least one equality}} \set{(x_1,x_2,x_3,x_4)}{|x_i|\le3\ (i=1,2,3)}

S

\set{(x_1,x_2,x_3,x_4)}{|x_i|>3 \mbox{ for at least one of }i=1,2,3}

S S \emptyset

\set{(x,y,z)}{z\ne1\mbox{ or }x^2+y^2>1}

open neither

closed

(\pi,1,0)

(1,0,e)

6 6 2\sqrt5 2L\sqrt n

\infty

\set{(x,y)}{x^2+y^2=1}

\dots if for A there is an integer R such that |\mathbf{X}_r|>A if r\ge R.

10 3 1 0 0

0

a/(1+a^2)

\infty \infty no -\infty

no

0 0 none 0

none

if D_f is unbounded and for each M there is an R such that f(\mathbf{X})>M if \mathbf{X}\in D_f and |\mathbf{X}|>R. Replace $>M$'' by<M’’ in

.

\lim_{\mathbf{X}\to\mathbf{0}}f(\mathbf{X})=0 if a_1+a_2+\cdots+a_n>b; no limit if a_1+a_2+\cdots+a_n\le b and a_1^2+a_2^2+\cdots+a_n^2\ne0; \lim_{\mathbf{X}\to\mathbf{0}}f(\mathbf{X})=\infty if a_1=a_2=\cdots=a_n=0 and b>0.

No; for example, \lim_{x\to\infty}g(x,\sqrt x)=0.

\mathbb R^3 \mathbb R^2 \mathbb R^3 \mathbb R^2 \set{(x,y)}{x\ge y}

\mathbb R^n

\mathbb R^3-\{(0,0,0)\} \mathbb R^2 \mathbb R^2 \mathbb R^2

\mathbb R^2

f(x,y)=xy/(x^2+y^2) if (x,y)\ne(0,0) and f(0,0)=0

\dst{\frac{2}{\sqrt3}(x+y\cos x-xy\sin x)-2\sqrt\frac{2}{3}(x\cos x)} \dst{\frac{1-2y}{\sqrt3}e^{-x+y^2+2z}} \dst{\frac{2}{\sqrt n}(x_1+x_2+\cdots+x_n)}

1/(1+x+y+z)

\phi_1^2\phi_2 -5\pi/\sqrt6 -2e 0

0

f_x=f_y=1/(x+y+2z), f_z=2/(x+y+2z)

f_x=2x+3yz+2y, f_y=3xz+2x, f_z=3xy f_x=e^{yz}, f_y=xze^{yz}, f_z=xye^{yz}

f_x=2xy\cos x^2y, f_y=x^2\cos x^2y, f_z=1

f_{xx}=f_{yy}=f_{xy}=f_{yx}=-1/(x+y+2z)^2, f_{xz}=f_{zx}=f_{yz}=f_{zy}= -2/(x+y+2z)^2, f_{zz}=-4/(x+y+2z)^2

f_{xx}=2, f_{yy}=f_{zz}=0, f_{xy}=f_{yx}=3z+2, f_{xz}=f_{zx}=3y, f_{yz}=f_{zy}=3x

f_{xx}=0, f_{yy}=xz^2e^{yz}, f_{zz}=xy^2e^{yz}, f_{xy}=f_{yx}=ze^{yz}, f_{xz}=f_{zx}=ye^{yz}, f_{yz}=f_{zy}=xe^{yz}

f_{xx}=2y\cos x^2y-4x^2y^2\sin x^2y, f_{yy}=-x^4\sin x^2y, f_{zz}=0, f_{xy}=f_{yx}=2x\cos x^2y-2x^3y\sin x^2y, f_{xz}=f_{zx}=f_{yz}=f_{zy}=0

f_{xx}(0,0)=f_{yy}(0,0)=0, f_{xy}(0,0)=-1, f_{yx}(0,0)=1\

f_{xx}(0,0)=f_{yy}(0,0)=0, f_{xy}(0,0)=-1, f_{yx}(0,0)=1

f(x,y)=g(x,y)+h(y), where g_{xy} exists everywhere and h is nowhere differentiable.

df=(3x^2+4y^2+2y\sin x+2xy\cos x)\,dx+(8xy+2x\sin x)\, dy,\ d_{\mathbf{X}_0}f=16\,dx, (d_{\mathbf{X}_0}f)(\mathbf{X}-\mathbf{X}_0)=16x \ df=-e^{-x-y-z}\,(dx+dy+dz), d_{\mathbf{X}_0}f=-dx-dy-dz, \ (d_{\mathbf{X}_0}f)(\mathbf{X}- \mathbf{X}_0)=-x-y-z \ df=(1+x_1+2x_2+\cdots+nx_n)^{-1}\sum_{j=1}^nj\,dx_j, d_{\mathbf{X}_0}f=\sum_{j=1}^n j\,dx_j, \ (d_{\mathbf{X}_0}f)(\mathbf{X}-\mathbf{X}_0)=\sum_{j=1}^n jx_j,\

df=2r|\mathbf{X}|^{2r-2}\sum_{j=1}^nx_j\,dx_j, d_{\mathbf{X}_0}f=2rn^{r-1}\sum_{j=1}^n dx_j, \ (d_{\mathbf{X}_0}f)(\mathbf{X}- \mathbf{X}_0)=2rn^{r-1}\sum_{j=1}^n (x_j-1),

The unit vector in the direction of (f_{x_1}(\mathbf{X}_0), f_{x_2}(\mathbf{X}_0), \dots,f_{x_n}(\mathbf{X}_0)) provided that this is not \mathbf{0}; if it is \mathbf{0}, then \partial f(\mathbf{X}_0)/\partial\boldsymbol{\Phi}=0 for every \boldsymbol{\Phi}.

z=2x+4y-6 z=2x+3y+1 z=(\pi x)/2+y-\pi/2

z=x+10y+4

5\,du+34\,dv 0 6\,du-18\,dv

8\,du

h_r=f_x\cos\theta+f_y\sin\theta, h_\theta=r(-f_x\sin\theta+f_y\cos\theta), h_z=f_z

h_r=f_x\sin\phi\cos\theta+f_y\sin\phi\sin\theta+f_z\cos\phi, h_\theta=r\sin\phi(-f_x\sin\theta+f_y\cos\theta), h_\phi=r(f_x\cos\phi\cos\theta+f_y\cos\phi\sin\theta-f_z\sin\phi)

h_y=g_xx_y+g_y+g_ww_y, h_z=g_xx_z+g_z+g_ww_z

h_{rr}=f_{xx}\sin^2\phi\cos^2\theta+f_{yy}\sin^2\phi\sin^2\theta+ f_{zz}\cos^2\phi+f_{xy}\sin^2\phi\sin2\theta+f_{yz}\sin2\phi\sin\theta+ f_{xz}\sin2\phi\cos\theta,

\dst h_{r\theta} =(-f_x\sin\theta+f_y\cos\theta)\sin\phi+\frac{r}{2}(f_{yy}- f_{xx})\sin^2\phi\sin2\theta +rf_{xy}\sin^2\phi\cos2\theta+\frac{r}{2} (f_{zy}\cos\theta-f_{zx}\sin\theta)\sin2\phi

\dst{1+x+\frac{x^2}{2}-\frac{y^2}{2}+\frac{x^3}{6}-\frac{xy^2}{2}}

\dst{1-x-y+\frac{x^2}{2}+xy+\frac{y^2}{2}-\frac{x^3}{6}-\frac{x^2y}{2} -\frac{xy^2}{2}-\frac{y^3}{6}}\ 0

xyz

(d_{(0,0)}^2p)(x,y)=(d_{(0,0)}^2q)(x,y)=2(x-y)^2

\left[\begin{array}{rrr}3&4&6\\2&-4&2\\7&2&3\end{array}\right]

\left[\begin{array}{rr}2&4\\3&-2\\7&-4\\6&1\end{array}\right]

\left[\begin{array}{rrrr}8&8&16&24\\0&0&4&12\\ 12&16&28&44\end{array}\right]

\left[\begin{array}{rrr}-2&-6&0\\0&-2&-4\\-2&2&-6\end{array}\right]

\left[\begin{array}{rrr}-2&2&6\\6&7&-3\\0&-2&6\end{array}\right]

\left[\begin{array}{rr}-1&7\\3&5\\5&14\end{array}\right]

\left[\begin{array}{rr}13&25\\16&31\\16&25\end{array}\right]

\left[\begin{array}{r}29\\50\end{array}\right]

\mathbf{A} and \mathbf{B} are square of the same order.

\left[\begin{array}{rrr}7&3&3\\4&7&7\\6&-9&1\end{array}\right]

\left[\begin{array}{rr}14&10\\6&-2\\14&2\end{array}\right]

\left[\begin{array}{rrr}-7&6&4\\-9&7&13\\5&0&-14\end{array}\right], \left[\begin{array}{rrr}-5&6&0\\4&-12&3\\4&0&3\end{array}\right]

\left[\begin{array}{rrr}6xyz&3xz^2&3x^2y\end{array}\right];
\left[\begin{array}{rrr}-6&3&-3\end{array}\right]

\cos(x+y)\left[\begin{array}{rr}1&1\end{array}\right]; \left[\begin{array}{rr}0&0\end{array}\right]

\left[\begin{array}{rrr}(1-xz)ye^{-xz}&xe^{-xz}&-x^2ye^{-xz} \end{array}\right]; \left[\begin{array}{rrr}2&1&-2\end{array}\right]\

\sec^2(x+2y+z)\left[\begin{array}{rrr}1&2&1\end{array}\right]; \left[\begin{array}{rrr}2&4&2\end{array}\right]

|\mathbf{X}|^{-1}\left[\begin{array}{rrrr}x_1&x_2&\cdots&x_n\end{array}\right]; \dst\frac{1}{\sqrt n}\left[\begin{array}{rrrr}1&1&\cdots&1\end{array}\right]

(2,3,-2) (2,3,0) (-2,0,-1)

(3,1,3,2)

\dst\frac{1}{10}\left[\begin{array}{rr}4&2\\-3&1\end{array}\right]

\dst\frac{1}{2}\left[\begin{array}{rrr}-1&1&2\\3&1&-4\\-1&-1&2 \end{array}\right]

\dst\frac{1}{25}\left[\begin{array}{rrr}4&3&-5\\6&-8&5\\-3&4&10 \end{array}\right]

\dst\frac{1}{2}\left[\begin{array}{rrr}1&-1&1\\-1&1&1\\1&1&-1 \end{array}\right]

\dst\frac{1}{7}\left[\begin{array}{rrrr}3&-2&0&0\\2&1&0&0\\0&0&2&-3 \\0&0&1&2\end{array}\right]

\dst\frac{1}{10}\left[\begin{array}{rrrr}-1&-2&0&5 \\-14&-18&10&20\\21&22&-10&-25\\17&24&-10&-25\end{array}\right]

\mathbf{F}'(\mathbf{X})=\left[\begin{array}{ccc} 2x&1&2\\-\sin(x+y+z)&-\sin(x+y+z)&-\sin(x+y+z)\\[2\jot] yze^{xyz}&xze^{xyz}&xye^{xyz}\end{array}\right];\[2] J\mathbf{F}(\mathbf{X})=e^{xyz}\sin(x+y+z) [x(1-2x)(y-z)-z(x-y)];\[2] \mathbf{G}(\mathbf{X})=\left[\begin{array}{r}0\\1\\1\end{array}\right] +\left[\begin{array}{rrr}2&1&2\\0&0&0\\0&0&-1\end{array}\right] \left[\begin{array}{c}x-1\\y+1\\z\end{array}\right]

\mathbf{F}'(\mathbf{X})=\left[\begin{array}{rr}e^x\cos y&-e^x\sin y\\e^x\sin y&e^x\cos y\end{array}\right]; J\mathbf{F}(\mathbf{X})=e^{2x};\[2] \mathbf{G}(\mathbf{X})=\left[\begin{array}{r}0\\1\end{array}\right] +\left[\begin{array}{rr}0&-1\\1&0\end{array}\right] \left[\begin{array}{c}x\\y-\pi/2\end{array}\right]\[2]

\mathbf{F}'(\mathbf{X})= \left[\begin{array}{rrr}2x&-2y&0\\0&2y&-2z\\-2x&0&2z\end{array}\right]; J\mathbf{F}=0;\[2] \mathbf{G}(\mathbf{X})= \left[\begin{array}{rrr}2&-2&0\\0&2&-2\\-2&0&2\end{array}\right] \left[\begin{array}{c}x-1\\y-1\\z-1\end{array}\right]

\mathbf{F}'(\mathbf{X})= \left[\begin{array}{ccc} (x+y+z+1)e^x&e^x&e^x\\(2x-x^2-y^2)e^{-x} &2ye^{-x}&0\end{array}\right]

\mathbf{F}'(\mathbf{X})=\left[\begin{array}{c}g_1'(x)\\g_2'(x)\\\vdots\\ g_n'(x)\end{array}\right] \

\mathbf{F}'(r,\theta)= \left[\begin{array}{ccc}e^x\sin yz&ze^x\cos yz&ye^x\cos yz\\ze^y\cos xz&e^y\sin xz&xe^y\cos xz\\ye^z\cos xy&xe^z\cos xy&e^z\sin xy\end{array}\right]

\mathbf{F}'(r,\theta)=\left[\begin{array}{rr}\cos\theta&-r\sin\theta \\\sin\theta&r\cos\theta\end{array}\right]; J\mathbf{F}(r,\theta)=r\[2]

\mathbf{F}'(r,\theta,\phi)=\left[\begin{array}{ccc}\cos\theta\cos\phi& -r\sin\theta\cos\phi&-r\cos\theta\sin\phi\\\sin\theta\cos\phi& \phantom{-}r\cos\theta\cos\phi&-r\sin\theta\sin\phi\\\sin\phi&0&r\cos\phi \end{array}\right];\ J\mathbf{F}(r,\theta,\phi)=r^2\cos\phi\[2]

\mathbf{F}'(r,\theta,z)=\left[\begin{array}{ccc}\cos\theta&-r\sin\theta&0 \\\sin\theta&\phantom{-}r\cos\theta&0\\0&0&1\end{array}\right]; J\mathbf{F}(r,\theta,z)=r

\left[\begin{array}{rrr}0&0&4\\0&-\frac{1}{2}&0\end{array}\right] \left[\begin{array}{rr}-18&0\\2&0\end{array}\right]

\left[\begin{array}{rr}9&-3\\3&-8\\1&0\end{array}\right]

\left[\begin{array}{rrr}4&-3&1\\0&1&1\end{array}\right] \left[\begin{array}{rr}2&0\\2&0\end{array}\right]

\left[\begin{array}{rr}5&10\\9&18\\-4&-8\end{array}\right]

[1,\pi/2] [1,2\pi] [1,\pi] [2\sqrt2,9\pi/4]

[\sqrt2,3\pi/4]

[1,-3\pi/2] [1,-2\pi] [1,-\pi] [2\sqrt2,-7\pi/4]

[\sqrt2,-5\pi/4]

Let f(x)=x\ (0\le x\le\frac{1}{2}), f(x)=x-\frac{1}{2}\ (\frac{1}{2}<x\le1); then f is locally invertible but not invertible on [0,1].

\mathbf{F}(S)=\set{(u,v)}{-\pi+2\phi<\arg(u,v)<\pi+2\phi}, where \phi is an argument of (a,b);

\mathbf{F}_S^{-1}(u,v)=(u^2+v^2)^{1/4} \left[\begin{array}{r}\cos(\arg(u,v)/2) \\[2\jot]\sin(\arg(u,v)/2)\end{array}\right],\ 2\phi-\pi<\arg(u,v)<2\phi+\pi

\left[\begin{array}{c}x\\y\end{array}\right]= \dst\frac{1}{10}\left[\begin{array}{c}\phantom{3}u-2v\\3u+4v\end{array}\right]; (\mathbf{F}^{-1})'=\dst\frac{1}{10} \left[\begin{array}{rr}1&-2\\3&4\end{array}\right]

\left[\begin{array}{c}x\\y\\z\end{array}\right]= \dst\frac{1}{2}\left[\begin{array}{c}u+2v+3w\\u-w\\u+v+2w\end{array}\right]; (\mathbf{F}^{-1})'=\dst\frac{1}{2} \left[\begin{array}{rrr}1&2&3\\1&0&-1\\1&1&2\end{array}\right]

\mathbf{G}_1(u,v)=\dst\frac{1}{\sqrt2} \left[\begin{array}{r}\sqrt{u+v}\\ \sqrt{u-v}\end{array}\right], \mathbf{G}_1'(u,v)=\dst\frac{1}{2\sqrt2} \left[\begin{array}{rr} 1/\sqrt{u+v}&1/\sqrt{u+v}\\ 1/\sqrt{u-v}&-1/\sqrt{u-v}\\ \end{array}\right]

\mathbf{G}_2(u,v)=\dst\frac{1}{\sqrt2} \left[\begin{array}{r}-\sqrt{u+v}\\ \sqrt{u-v}\end{array}\right], \mathbf{G}_2'(u,v)=\dst\frac{1}{2\sqrt2} \left[\begin{array}{rr} -1/\sqrt{u+v}&-1/\sqrt{u+v}\\ 1/\sqrt{u-v}&-1/\sqrt{u-v}\\ \end{array}\right]

\mathbf{G}_3(u,v)=\dst\frac{1}{\sqrt2} \left[\begin{array}{r}\sqrt{u+v}\\ -\sqrt{u-v}\end{array}\right], \mathbf{G}_3'(u,v)=\dst\frac{1}{2\sqrt2} \left[\begin{array}{rr} 1/\sqrt{u+v}&1/\sqrt{u+v}\\ -1/\sqrt{u-v}&1/\sqrt{u-v}\\ \end{array}\right]

\mathbf{G}_4(u,v)=\dst\frac{1}{\sqrt2} \left[\begin{array}{r}-\sqrt{u+v}\\ -\sqrt{u-v}\end{array}\right], \mathbf{G}_4'(u,v)=\dst\frac{1}{2\sqrt2} \left[\begin{array}{rr} -1/\sqrt{u+v}&-1/\sqrt{u+v}\\ -1/\sqrt{u-v}&1/\sqrt{u-v}\\ \end{array}\right]

From solving x=r\cos\theta, y=r\sin\theta for \theta=\arg(x,y). Each equation is satisfied by angles that are not arguments of (x,y), since none of the formulas identifies the quadrant of (x,y) uniquely. Moreover,

does not hold if x=0.

\left[\begin{array}{c}x\\y\end{array}\right]= \mathbf{G}(u,v)=(u^2+v^2)^{1/4} \left[\begin{array}{r}\cos[\frac{1}{2}\arg(u,v)] \\[2\jot] \sin(\arg(u,v)/2)\end{array}\right],

where \beta-\pi/2<\arg(u,v)<\beta+\pi/2 and \beta is an argument of (a,b);

\mathbf{G}'(u,v)=\dst\frac{1}{2(x^2+y^2)} \left[\begin{array}{rr}x&y\\-y&x\end{array}\right]

If \mathbf{F}(x_1,x_2, \dots,x_n)=(x_1^3,x_2^3, \dots,x_n^3), then \mathbf{F} is invertible, but\ J\mathbf{F}(\mathbf{0})~=0.

\mathbf{A}(\mathbf{U})= \left[\begin{array}{r}1\\-1\end{array}\right] -\dst\frac{1}{25}\left[\begin{array}{rr}5&5\\3&8\end{array}\right] \left[\begin{array}{c}u+5\\v-4\end{array}\right]

\mathbf{A}(\mathbf{U})= \left[\begin{array}{r}1\\1\end{array}\right] +\dst\frac{1}{6}\left[\begin{array}{rr}4&-2\\-3&3\end{array}\right] \left[\begin{array}{c}u-2\\v-3\end{array}\right]

\mathbf{A}(\mathbf{U})= \left[\begin{array}{r}0\\1\\1\end{array}\right]+ \left[\begin{array}{rrr}0&-1&1\\-1&1&0\\1&0&0\end{array}\right] \left[\begin{array}{c}u-1\\v-1\\w-2\end{array}\right]

\mathbf{A}(\mathbf{U})= \left[\begin{array}{c}1\\\pi/2\\\pi\end{array}\right]+ \left[\begin{array}{rrr}0&-1&0\\1&0&0\\0&0&-1\end{array}\right] \left[\begin{array}{c}u\\v+1\\w\end{array}\right]

\mathbf{G}'(x,y,z)= \left[\begin{array}{ccc} \cos\theta\cos\phi&\sin\theta\cos\phi&\sin\phi\\[2\jot] -\dst\frac{\sin\theta}{ r\cos\phi}&\dst\frac{\cos\theta}{ r\cos\phi}&0\\[2\jot] -\dst\frac{1}{ r}\cos\theta\sin\phi&-\dst\frac{1}{ r}\sin\theta\sin\phi&\dst\frac{1}{ r}\cos\phi\end{array}\right]

\mathbf{G}'(x,y,z)= \left[\begin{array}{ccc}\cos\theta&\sin\theta&0\\[2\jot] -\dst\frac{1}{ r}\sin\theta&\dst\frac{1}{ r}\cos\theta&0\\[2\jot] 0&0&1\end{array}\right]

\left[\begin{array}{c}u\\v\end{array}\right]= \dst\frac{1}{2}\left[\begin{array}{rr}-3&4\\1&-2\end{array}\right] \left[\begin{array}{c}x\\y\end{array}\right]

\left[\begin{array}{c}u\\v\\w\end{array}\right]=\dst -\frac{1}{2} \left[\begin{array}{rr} 3&3\\-1&2\\2&3 \end{array}\right] \left[\begin{array}{c}x\\y\end{array}\right]

\left[\begin{array}{c}u\\v\end{array}\right]= \dst\frac{1}{5}\left[\begin{array}{rr}2&-1\\-1&3\end{array}\right] \left[\begin{array}{c}-y+\sin x\\-x+\sin y\end{array}\right]

u=-x, v=-y, z=-w

f_i(\mathbf{X},\mathbf{U})=\dst\left(\sum_{j=1}^n a_{ij}(x_j-x_{j0})\right)^r-(u_i-u_{i0})^s, 1\le i\le m, where r and s are positive integers and not all a_{ij}=0. r=s=3; r=1, s=3;

r=s=2

u_x(1,1)=-\frac{5}{8}, u_y(1,1)=-\frac{1}{2}

u_x(1,1,1)=\frac{5}{8}, u_y(1,1,1)=-\frac{9}{8}, u_z(1,1,1)=\frac{1}{2}

u(1,2)=0, u_x(1,2)=u_y(1,2)=-4

u(-1,-2)=2, u_x(-1,-2)=1, u_y(-1,-2)=-\frac{1}{2}

u(\pi/2,\pi/2)=u_x(\pi/2,\pi/2)=u_y(\pi/2,\pi/2)=0

u(1,1)=1, u_x(1,1)=u_y(1,1)=-1

u_1(1,1)=1,\dst\frac{\partial u_1(1,1)}{\partial x}=5, \dst\frac{\partial u_1(1,1)}{\partial y}=2

u_2(1,1)=2, \dst\frac{\partial u_2(1,1)}{\partial x}=-14; \dst\frac{\partial u_2(1,1)}{\partial y}=-2

u_k(0,\pi)=(2k+1)\pi/2, \dst\frac{\partial u_k(0,\pi)}{\partial x}=0, \dst\frac{\partial u_k(0,\pi)}{\partial y}=-1,k= integer

\dst\frac{1}{5}\left[\begin{array}{rrr}-1&-2&1\\-1&-2&1\end{array}\right] u'(0)=3, v'(0)=-1

\dst\frac{1}{6}\left[\begin{array}{rr}5&5\\-5&-5\\6&6\end{array}\right]

\mathbf{U}_1(1,1)=\left[\begin{array}{r}3\\1\end{array}\right], \mathbf{U}_1'(1,1)=\left[\begin{array}{rr}1&3\\-1&2\end{array}\right];

\mathbf{U}_2(1,1)=-\left[\begin{array}{r}3\\1\end{array}\right], \mathbf{U}_2'(1,1)=-\left[\begin{array}{rr}1&3\\-1&2\end{array}\right]

u_x(0,0,0)=2, v_x(0,0,0)= w_x(0,0,0)=-2

y_x=-\dst\frac{\dst\frac{\partial(f,g,h)}{\partial(x,z,u)}}{ \dst\frac{\partial(f,g,h)}{\partial(y,z,u)}}, y_v=-\dst\frac{\dst\frac{\partial(f,g,h)}{\partial(v,z,u)}}{ \dst\frac{\partial(f,g,h)}{\partial(y,z,u)}}, z_x=-\dst\frac{\dst\frac{\partial(f,g,h)}{\partial(y,x,u)}}{ \dst\frac{\partial(f,g,h)}{\partial(y,z,u)}},

z_v= -\dst\frac{\dst\frac{\partial(f,g,h)}{\partial(y,v,u)}}{ \dst\frac{\partial(f,g,h)}{\partial(y,z,u)}}, u_x=-\dst\frac{\dst\frac{\partial(f,g,h)}{\partial(y,z,x)}}{ \dst\frac{\partial(f,g,h)}{\partial(y,z,u)}}, u_v=-\dst\frac{\dst\frac{\partial(f,g,h)}{\partial(y,z,v)}}{ \dst\frac{\partial(f,g,h)}{\partial(y,z,u)}}

x=-2y-u, z=-2v; x=-2y-u, v=-\dst\frac{z}{2}; y=-\dst\frac{x}{2}-\dst\frac{u}{2}, z=-2v; y=-\dst\frac{x}{2}-\dst\frac{u}{2}, v=-\dst\frac{z}{2}; z=-2v, u=-x-2y; u=-x-2y, v=-\dst\frac{z}{2}

y_x(1,-1,-2)=-\frac{1}{2}, v_u(1,-1,-2)=1

u_w(0,-1)=\frac{5}{6}, u_y(0,-1)=0, v_w(0,-1)=-\frac{5}{6}, v_y(0,-1)=0,\ x_w(0,-1)=1, x_y(0,-1)=-1

u_x(1,1)=0, u_y(1,1)=0, v_x(1,1)=-1, v_y(1,1)=-1, u_{xx}(1,1)=2,\ u_{xy}(1,1)=1, u_{yy}(1,1)=2, v_{xx}(1,1)=-2, v_{xy}(1,1)=-1, v_{yy}(1,1)=-2

u_x(1,-1)=0, u_y(1,-1)=\dst\frac{1}{2}, v_x(1,-1)=-\dst\frac{1}{2}, v_y(1,-1)=0,\ u_{xx}(1,-1)=-\dst\frac{1}{8}, u_{xy}(1,-1)=\dst\frac{1}{8}, u_{yy}(1,-1)=\dst\frac{1}{8}, v_{xx}(1,-1)=-\dst\frac{1}{8},\ v_{xy}(1,-1)=-\dst\frac{1}{8}, v_{yy}(1,-1)=\dst\frac{1}{8}

28

\frac{1}{4} 3(b-a)(d-c), 0 \set{(m,n)}{m,n=\mbox{integers}}

12 \frac{79}{20} -1

(1-\log2)/2

\frac{7}{4} 17 \frac{2}{3}(\sqrt2-1)

1/4\pi

\frac{3}{8}, \frac{5}{8} \frac{3}{8}, \frac{5}{8} \frac{3}{4}, \frac{5}{4} \frac{3}{4}\left(z+\frac{1}{2}\right), \frac{5}{4}\left(z+\frac{1}{2}\right)

z+\frac{1}{2}, 1

-285 0 0

\frac{1}{4}(e-\frac{5}{2})

324 \frac{1}{6}

1 \frac{52}{15}

36 1 \frac{64}{3}

(e^6+17)/2

\frac{2}{27} \frac{1}{2}(e-\frac{5}{2}) \frac{1}{24}

\frac{1}{36}

16\pi \frac{1}{6} \frac{128}{21}

\frac{\pi}{2}

\frac{1}{2}(b_1-a_1)\cdots(b_n-a_n)\sum_{j=1}^n(a_j+b_j)

\frac{1}{3}(b_1-a_1)\cdots(b_n-a_n)\sum_{j=1}^n(a_j^2+a_jb_j+b_j^2)

2^{-n}(b_1^2-a_1^2)\cdots(b_n^2-a_n^2)

\int_{-\sqrt3/2}^{\sqrt3/2}dx\int_{1/2}^{\sqrt{1-x^2}}f(x,y)\,dy \frac{1}{2}

Let S_1 and S_2 be dense subsets of \mathbb R such that S_1\cup S_2=\mathbb R.

-1; c (constant); 1 (u_2-u_1)(v_2-v_1)/|ad-bc|

\frac{5}{6} \frac{4}{9}

\log\frac{5}{2} 3 \frac{1}{2} \frac{5}{4}e(e-1)

\frac{4}{3}\pi abc 2\pi(e^{25}-e^9) 16\pi/3 21/64

(\pi/8)\log5 (\pi/4)(e^4-1)

2\pi/15

\pi^2a^4/2

(\beta_1-\alpha_1)\cdots(\beta_n-\alpha_n)/|\det(\mathbf{A})| |a_1a_2\cdots a_n|V_n

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{}

Suppose f\in C[a,b]. Acording to the , if \epsilon>0, there is a polynonmial p such that |f(x)-p(x)|<\epsilon, a\le x\le b. Now suppose that a\le x_{1n} < x_{2n}<\cdots<x_{nn}\le b,\quad a\le y_{1n} < y_{2n}<\cdots<y_{nn}\le b,\quad n\ge 1. \nonumber and \lim_{n\to\infty}\frac{1}{n}\sum_{i=1}^{n}|x_{in}-y_{in}|=0. \nonumber Show that if f\in C[a,b], then \lim_{n\to\infty}\frac{1}{n}\sum_{i=1}^{n}|f(x_{in})-f(y_{in})|=0. \nonumber

By the triangle inequality, |f(x_{in})-f(y_{in})|\le |f(x_{in})-p(x_{in})| +|p(x_{in})-p(y_{in})|+|p(y_{in})-f(y_{in})|, \nonumber so \begin{equation} \tag{A} |f(x_{in})-f(y_{in})|<|p(x_{in})-p(y_{in})|+2\epsilon. \end{equation} \nonumber Let M=\max_{a\le x\le b}|p'(x)|. By the mean value theorem, |p(x_{in})-p(y_{in})|\le M |x_{in}-y_{in}|. \nonumber This and (A) imply that \frac{1}{n}\sum_{i=1}^n|f(x_{in})-f(y_{in})|< 2\epsilon+\frac{M}{n}\sum_{i=1}^n|x_{in}-y_{in}|. \nonumber From this and (A), \limsup_{n\to\infty} \frac{1}{n}\sum_{i=1}^n|f(x_{in})-f(y_{in})|\le 2\epsilon. \nonumber Since \epsilon is arbitrary, this implies the conclusion.

{} In the setting of Exercise~1, let y_{in}=a+\frac{i}{n}\sum_{i=1}^{n}(b-a), \quad 1\le i\le n,\quad n\ge 1. \nonumber Show that \lim_{n\to\infty}\frac{1}{n}\sum_{i=1}^{n} f(x_{in})=\frac{1}{b-a}\int_{a}^{b}f(x)\,dx. \nonumber

{Solution 2.} Since f\in C[a,b], \int_{a}^{b}f(x)\,dx exists (Theorem~3.2.8, p.~133).

Therefore, from Definition~3.1.1 (p.114), \lim_{n\to\infty}\sum_{i=1}^{n} f(y_{in})=\frac{1}{b-a}\int_{a}^{b}f(x)\,dx. \nonumber Since \frac{1}{n}\left| \sum_{i=1}^{n}f(x_{in})-\frac{1}{b-a}\int_{a}^{b}f(x)\,dx\right|\le \frac{1}{n}\sum_{i=1}^{n}|f(x_{in})-f(y_{in})|+ \left|\frac{1}{n} \sum_{i=1}^{n}f(y_{in})-\frac{1}{b-a}\int_{a}^{b}f(x)\,dx\right|, \nonumber Exercise1 implies the conclusion.

Suppose g is continuous and nondecreasing on [c,d]. For

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