Big Ideas Math - Algebra 1, A Common Core Curriculum

Published by Big Ideas Learning LLC
ISBN 10: 978-1-60840-838-2
ISBN 13: 978-1-60840-838-2

Chapter 5 - Solving Systems of Linear Equations - Chapter Review - Page 283: 9

Answer

The solution is $(-2,5)$.

Work Step by Step

The given system of equations is $x+6y=28$ ...... (1) $2x-3y=-19$ ...... (2) Multiply equation (2) by $2$. $\Rightarrow 2(2x-3y)=2(-19)$ Use distributive property. $\Rightarrow 4x-6y=-38$ ...... (3) Add equation (1) and (3). $\Rightarrow x+6y+4x-6y=28-38$ Add like terms. $\Rightarrow 5x=-10$ Divide each side by $5$. $\Rightarrow \frac{5x}{5}=-\frac{10}{5}$ Simplify. $\Rightarrow x=-2$ Substitute $-2$ for $x$ in equation (1). $\Rightarrow -2+6y=28$ Add $2$ to each side. $\Rightarrow -2+6y+2=28+2$ Simplify. $\Rightarrow 6y=30$ Divide each side by $6$. $\Rightarrow \frac{6y}{6}=\frac{30}{6}$ Simplify. $\Rightarrow y=5$ Check $(x,y)=(-2,5)$ Equation (1): $\Rightarrow x+6y=28$ $\Rightarrow -2+6(5)=28$ $\Rightarrow -2+30=28$ $\Rightarrow 28=28$ True. Equation (2): $\Rightarrow 2x-3y=-19$ $\Rightarrow 2(-2)-3(5)=-19$ $\Rightarrow -4-15=-19$ $\Rightarrow -19=-19$ True. Hence, the solution is $(-2,5)$.
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