Elementary Technical Mathematics

Published by Brooks Cole
ISBN 10: 1285199197
ISBN 13: 978-1-28519-919-1

Chapter 9 - Section 9.2 - Solving Pairs of Linear Equations by Addition - Exercises - Page 332: 17


One common solution $\Rightarrow$ $(7,-5)$

Work Step by Step

We use the addition method below: We add the 2 equations: $x+2y=-3$ $2x+y=9$ Multiply both sides of the 1st equation by $-2$ to cancel $x$. $-2x-4y=6$ $\underline{+2x+y=9}$ $-3y=15$ Solve for $y$: $y=\frac{15}{-3}=-5$ Substitute into any of the 2 equations and solve for $x$: $x+2y=-3$ $x+2(-5)=-3$ $x-10=-3$ $x=10-3$ $x=7$
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