Intermediate Algebra (12th Edition)

Published by Pearson
ISBN 10: 0321969359
ISBN 13: 978-0-32196-935-4

Chapter 8 - Chapter R-8 - Cumulative Review Exercises - Page 578: 17

Answer

$(1,-2)$

Work Step by Step

Multiplying the first equation by $3$ and multiplying the second equation by $4$, the given system \begin{align*}\require{cancel} 2x-4y&=10 \\ 9x+3y&=3 \end{align*}is equivalent to \begin{align*}\require{cancel} 6x-12y&=30 \\ 36x+12y&=12 .\end{align*} Adding the two equations above results to \begin{align*}\require{cancel} 42x&=42 \\\\ \dfrac{\cancel{42}x}{\cancel{42}}&=\dfrac{42}{42} \\\\ x&=1 .\end{align*} Substituting $x=1$ into the first equation, $(2x-4y=10)$, results to \begin{align*}\require{cancel} 2(1)-4y&=10 \\ 2-4y&=10 \\ -4y&=10-2 \\ -4y&=8 \\\\ \dfrac{\cancel{-4}y}{\cancel{-4}}&=\dfrac{8}{-4} \\\\ y&=-2 .\end{align*} Hence, the solution of the given system is $(x,y)=(1,-2)$.
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