Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 7 - Algebra: Graphs, Functions, and Linear Systems - 7.4 Linear Inequalities in Two Variables - Exercise Set 7.4 - Page 454: 42

Answer

See below:

Work Step by Step

Let one variable be x and another variable be y. Sum of two variables is at most 3, which gives \[x+y\le 3\](1) The sum ofvariable y with 4 times the variable x does not exceed 6, which gives \[4x+y\le 6\](2) Both the inequalities in equation (1) and equation (2) are of the same sign. So, treat the equation as equality problem, which gives \[x+y=3\] (3) \[4x+y=6\] (4) Subtract equation (3) from (4) by elimination process to get \[\begin{align} & 3x=3 \\ & x=1 \end{align}\] Put the value of \[x=1\]in\[x+y=3\], which gives \[\begin{align} & 1+y=3 \\ & y=2 \end{align}\] Both the equations intersect at\[\left( 1,2 \right)\]. Put \[y=0\], which gives the x-intercept. So, the x-intercept for equation (3) is \[\begin{align} & x+y=3 \\ & x+0=3 \\ & x=3 \end{align}\] Put \[x=0\], which gives the y-intercept. The y-intercept for equation (3) is \[\begin{align} & x+y=3 \\ & 0+y=3 \\ & y=3 \end{align}\] Similarly, the x-intercept for equation (4) is \[\begin{align} & 4x+y=6 \\ & 4x+0=6 \\ & x=\frac{6}{4} \\ & x=1.5 \end{align}\] The y-intercept for equation (4) is \[\begin{align} & 4x+y=6 \\ & 4\left( 0 \right)+y=6 \\ & 0+y=6 \\ & y=6 \end{align}\] Now, take test point for equation (1): Let test point be \[\left( 0,0 \right)\]. Put it in equation (1), which gives \[\begin{align} & x+y\le 3 \\ & 0+0\le 3 \\ & 0\le 3 \end{align}\] The above statement is true. The shaded region contains the test point\[\left( 0,0 \right)\]. Hence, the shaded region is given as
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