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 - 5.3 - Solving Systems of Linear Equations by Elimination - Exercises - Page 251: 15

Answer

The solution is $(-7,-12)$.

Work Step by Step

The given system of equations is $4x-3y=8$ ...... (1) $5x-2y=-11$ ...... (2) Multiply each side of equation (1) by $-2$. $-2(4x-3y)=-2(8)$ Simplify. $-8x+6y=-16$ ...... (3) Multiply each side of equation (2) by $3$. $3(5x-2y)=3(-11)$ Simplify. $15x-6y=-33$ ...... (4) Add equation (3) and (4). $\Rightarrow -8x+6y+15x-6y=-16-33$ Add like terms. $\Rightarrow 7x=-49$ Divide each side by $7$. $\Rightarrow \frac{7x}{7}=\frac{-49}{7}$ Simplify. $\Rightarrow x=-7$ Substitute $-7$ for $x$ in equation (1). $\Rightarrow 4(-7)-3y=8$ Simplify. $\Rightarrow -28-3y=8$ Add $28$ to each side. $\Rightarrow -28-3y+28=8+28$ Simplify. $\Rightarrow -3y=36$ Divide each side by $-3$. $\Rightarrow \frac{-3y}{-3}=\frac{36}{-3}$ Simplify. $\Rightarrow y=-12$ Check $(x,y)=(-7,-12)$ Equation (1): $\Rightarrow 4x-3y=8$ $\Rightarrow 4(-7)-3(-12)=8$ $\Rightarrow -28+36=8$ $\Rightarrow 8=8$ True. Equation (2): $\Rightarrow 5x-2y=-11$ $\Rightarrow 5(-7)-2(-12)=-11$ $\Rightarrow -35+24=-11$ $\Rightarrow -11=-11$ True. Hence, the solution is $(-7,-12)$.
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