Intermediate Algebra: Connecting Concepts through Application

Published by Brooks Cole
ISBN 10: 0-53449-636-9
ISBN 13: 978-0-53449-636-4

Chapter 2 - Systems of Linear Equations and Inequalities - 2.3 Solving Systems of Equations Using the Elimination Method - 2.3 Exercises - Page 160: 2

Answer

$(4, -9)$

Work Step by Step

Add the equations together: \begin{array}\\ 6x+2y=6\\ \underline{-6x-5y=21}\\ 0x-3y=27\\\\ \end{array} Solve for $y$ to obtain: \begin{align*} -3y&=27\\ y&=\frac{27}{-3}\\ y&=-9\end{align*} Substitute $-9$ to $y$ in the first equation to obtain: \begin{align*} 6x+2y&=6\\ 6x+2(-9)&=6\\ 6x-18&=6\\ 6x&=6+18\\ 6x&=24 x&=\frac{24}{6}\\ x&=4 \end{align*} Check by substituting $4$ to $x$ and $-9$ to $y$ in the second equation to obtain: \begin{align*} -6(4)-5(-9)&=21\\ -24+45&=21\\ 21&\stackrel{\checkmark}=21 \end{align*} Therefore, the solution is $(4, -9)$.
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