5.3E: Exercises
- Page ID
- 128890
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In exercises 1 - 7, plot the point whose polar coordinates are given by first constructing the angle \( \theta \) and then marking off the distance \(r\) along the ray.
1) \(\left(3,\frac{ \pi }{6}\right)\)
- Answer
2) \(\left(−2,\frac{5 \pi }{3}\right)\)
3) \(\left(0,\frac{7 \pi }{6}\right)\)
- Answer
4) \(\left(−4,\frac{3 \pi }{4}\right)\)
5) \(\left(1,\frac{ \pi }{4}\right)\)
- Answer
6) \(\left(2,\frac{5 \pi }{6}\right)\)
7) \(\left(1,\frac{ \pi }{2}\right)\)
- Answer
In exercises 8 - 11, consider the polar graph below. Give two sets of polar coordinates for each point.
8) Coordinates of point A.
9) Coordinates of point B.
- Answer
- \(B\left(3,\frac{− \pi }{3}\right) B\left(−3,\frac{2 \pi }{3}\right)\)
10) Coordinates of point C.
11) Coordinates of point D.
- Answer
- \(D\left(5,\frac{7 \pi }{6}\right) D\left(−5,\frac{ \pi }{6}\right)\)
In exercises 12 - 17, the rectangular coordinates of a point are given. Find two sets of polar coordinates for the point in \((0,2 \pi ]\). Round to three decimal places.
12) \((2,2)\)
13) \((3,−4)\)
- Answer
- \((5,−0.927),\;(−5,−0.927+ \pi )\)
14) \((8,15)\)
15) \((−6,8)\)
- Answer
- \((10,−0.927),\;(−10,−0.927+ \pi )\)
16) \((4,3)\)
17) \((3,−\sqrt{3})\)
- Answer
- \((2\sqrt{3},−0.524),\;(−2\sqrt{3},−0.524+ \pi )\)
In exercises 18 - 24, find rectangular coordinates for the given point in polar coordinates.
18) \(\left(2,\frac{5 \pi }{4}\right)\)
19) \(\left(−2,\frac{ \pi }{6}\right)\)
- Answer
- \((−\sqrt{3},−1)\)
20) \(\left(5,\frac{ \pi }{3}\right)\)
21) \(\left(1,\frac{7 \pi }{6}\right)\)
- Answer
- \(\left(−\frac{\sqrt{3}}{2},\frac{−1}{2}\right)\)
22) \(\left(−3,\frac{3 \pi }{4}\right)\)
23) \(\left(0,\frac{ \pi }{2}\right)\)
- Answer
- \((0,0)\)
24) \((−4.5,6.5)\)
In exercises 25 - 29, determine whether the graphs of the polar equation are symmetric with respect to the \(x\)-axis, the \(y\) -axis, or the origin.
25) \(r=3\sin(2 \theta )\)
- Answer
- Symmetry with respect to the x-axis, y-axis, and origin.
26) \(r^2=9\cos \theta \)
27) \(r=\cos\left(\frac{ \theta }{5}\right)\)
- Answer
- Symmetric with respect to x-axis only.
28) \(r=2\sec \theta \)
29) \(r=1+\cos \theta \)
- Answer
- Symmetry with respect to x-axis only.
In exercises 30 - 33, describe the graph of each polar equation. Confirm each description by converting into a rectangular equation.
30) \(r=3\)
31) \( \theta =\frac{ \pi }{4}\)
- Answer
- Line \(y=x\)
32) \(r=\sec \theta \)
33) \(r=\csc \theta \)
- Answer
- \(y=1\)
In exercises 34 - 36, convert the rectangular equation to polar form and sketch its graph.
34) \(x^2+y^2=16\)
35) \(x^2−y^2=16\)
- Answer
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Hyperbola; polar form \(r^2\cos(2 \theta )=16\) or \(r^2=16\sec \theta .\)
36) \(x=8\)
In exercises 37 - 38, convert the rectangular equation to polar form and sketch its graph.
37) \(3x−y=2\)
- Answer
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\(r=\frac{2}{3\cos \theta −\sin \theta }\)
38) \(y^2=4x\)
In exercises 39 - 43, convert the polar equation to rectangular form and sketch its graph.
39) \(r=4\sin \theta \)
40) \(x^2+y^2=4y\)
- Answer
41) \(r=6\cos \theta \)
42) \(r= \theta \)
- Answer
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\(x\tan\sqrt{x^2+y^2}=y\)
43) \(r=\cot \theta \csc \theta \)
In exercises 44 - 54, sketch a graph of the polar equation and identify any symmetry.
44) \(r=1+\sin \theta \)
- Answer
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\(y\)-axis symmetry
45) \(r=3−2\cos \theta \)
46) \(r=2−2\sin \theta \)
- Answer
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\(y\)-axis symmetry
47) \(r=5−4\sin \theta \)
48) \(r=3\cos(2 \theta )\)
- Answer
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\(x\)-and \(y\)-axis symmetry and symmetry about the pole
49) \(r=3\sin(2 \theta )\)
50) \(r=2\cos(3 \theta )\)
- Answer
- \(x\)-axis symmetry
51) \(r=3\cos\left(\frac{ \theta }{2}\right)\)
52) \(r^2=4\cos\left(\frac{2}{ \theta }\right)\)
- Answer
-
\(x\)-and \(y\)-axis symmetry and symmetry about the pole
53) \(r^2=4\sin \theta \)
54) \(r=2 \theta \)
- Answer
- no symmetry
55) [Technology Required] The graph of \(r=2\cos(2 \theta )\sec( \theta ).\) is called a strophoid. Use a graphing utility to sketch the graph, and, from the graph, determine the asymptote.
56) [Technology Required] Use a graphing utility and sketch the graph of \(r=\dfrac{6}{2\sin \theta −3\cos \theta }\).
- Answer
- a line
57) [Technology Required] Use a graphing utility to graph \(r=\frac{1}{1−\cos \theta }\).
58) [Technology Required] Use technology to graph \(r=e^{\sin( \theta )}−2\cos(4 \theta )\).
- Answer
59) [Technology Required] Use technology to plot \(r=\sin(\frac{3 \theta }{7})\) (use the interval \(0 \leq \theta \leq 14 \pi \)).
60) Without using technology, sketch the polar curve \( \theta =\frac{2 \pi }{3}\).
- Answer
61) [Technology Required] Use a graphing utility to plot \(r= \theta \sin \theta \) for \(− \pi \leq \theta \leq \pi \).
62) [Technology Required] Use technology to plot \(r=e^{−0.1 \theta }\) for \(−10 \leq \theta \leq 10.\)
- Answer
63) [Technology Required] There is a curve known as the “Black Hole.” Use technology to plot \(r=e^{−0.01 \theta }\) for \(−100 \leq \theta \leq 100\).
64) [Technology Required] Use the results of the preceding two problems to explore the graphs of \(r=e^{−0.001 \theta }\) and \(r=e^{−0.0001 \theta }\) for \(| \theta |>100\).
- Answer
- Answers vary. One possibility is the spiral lines become closer together and the total number of spirals increases.