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: 19


One common solution $\Rightarrow$ $(4,-1)$

Work Step by Step

We use the addition method below: We add the 2 equations: $3x+5y=7$ $2x-7y=15$ Multiply both sides of the 1st equation by $2$ to cancel $x$. Multiply both sides of the 2nd equation by $-3$ to cancel $x$. We get: $+6x+10y=14$ $\underline{-6x+21y=-45}$ $31y=-31$ Solve for $y$ and simplify: $y=\frac{-31}{31}=-1$ Substitute into any of the 2 equations and solve for $x$: $3x+5y=7$ $3x+5(-1)=7$ $3x-5=7$ $3x=7+5$ $3x=12$ $x=\frac{12}{3}$ $x=4$
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