2.3: Arithmetic of inequality
- Page ID
- 7427
This page is a draft and is under active development.
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Definition: Inequality
Let \(a, b\in \mathbb{Z}\). Then
- \(a< b\) provided \(b=a + k\), for some \(k \in \mathbb{Z_+}\).
- \(a> b\) provided \(a=b + h\), for some \(h \in \mathbb{Z_+}\).
Theorem \(\PageIndex{1}\)
Let \(a, b\in \mathbb{Z}\).
- If \(a< b\) then \(a+c< b+c\), \( \forall c \in \mathbb{Z}\).
- If \(a< b\) then \(ac< bc\),\( \forall c \in \mathbb{Z_+}\).
- If \(a< b\) then \(ac> bc\),\( \forall c \in \mathbb{Z_-}\).
- If \(a< b\) and \(c< d\) then \(a+c< b+d\).
- Proof
-
Let \(a, b, c \in \mathbb{Z}\) such that \(a <b\). Then \(b=a + k\), for some \(k \in \mathbb{Z_+}\).
1. Now consider, \(b+c= (a+k)+c= (a+c)+k\), for some \(k \in \mathbb{Z_+}\). Thus \(a+c< b+c\).
2.
Example \(\PageIndex{1}\):
Determine all integers \(m\) that satisfy \(-12m \geq 324\).
Solution
Since \(-12m \geq 324\), \( m \leq -\dfrac{324}{12}=-27\).
Example \(\PageIndex{2}\):
Determine all integers \(m\) that satisfy \(14m \geq 635\).
Solution
Since \(14m \geq 635\), \( m \geq \dfrac{635}{14}=45.35\). Thus the solutions are \( \{m\in \mathbb{Z}| m\geq 46\}.\)
Example \(\PageIndex{3}\):
Determine all integers \(k\) that satisfy \( -165+ 98k \geq 0, -335+199k \geq 0, -165+ 98k < 100 \) and \( -335+199k <100\).
Solution
Since \(-165 + 98k ≥ 0, k ≥ 1.68\).
Since \(-335 + 199k ≥ 0, k ≥ 1.68\).
Since \(-165 + 98k < 100, 98k < 265, \) and \( k < 2.70.\)
Since \(-335 + 199k < 100, 199k < 435,\) and \( k < 2.18.\)
Since \( 1.68 ≤ k < 2.18\) and \( k ∈ ℤ, k = 2. \)