Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

Published by Pearson
ISBN 10: 0-32193-104-1
ISBN 13: 978-0-32193-104-7

Chapter 10 - Systems of Equations and Inequalities - Section 10.1 Systems of Linear Equations: Substitution and Elimination - 10.1 Assess Your Understanding - Page 734: 28

Answer

$x= 1, y= -\dfrac{4}{3} \text{ or } \left(1, -\dfrac{4}{3}\right)$

Work Step by Step

The system of equations is given by the following two equations: $$\begin{cases} 3x+3y=-1 \hspace{20pt} (1)\\[3mm] 4x+y=\dfrac{8}{3} \hspace{20pt} (2) \end{cases}$$ Multiply equation $ (2)$ by $-3$ so that the coefficients of y in the two equations are additive inverses: $-12x-3y=-8\hspace{20pt} (1)$ $\text{Add the two equations to eliminate y:}$ \[ \begin{aligned} 3x+3y&=-1 \\[2mm] -12x-3y&=-8 \\[3mm] \hline -9x&=-9 \\[2mm] \end{aligned} \] Divide both sides by $-9$ to obtain: $x=1$ $\text{Substituting in equation (2) for }x=1$ gives: $4(1)+y=\dfrac{8}{3}$ $y=\dfrac{8}{3}-4$ $y= -\dfrac{4}{3}$ $\boxed{x= 1 \hspace{20pt} y= -\dfrac{4}{3}}$
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