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: 35

Answer

$x=4, y = 3\text{ or } (4, 3)$

Work Step by Step

The system of equations is given by the following two equations: $$\begin{cases} \dfrac{1}{2}x+\dfrac{1}{3}y=3\hspace{20pt} &(1)\\[3mm] \dfrac{1}{4}x-\dfrac{2}{3}y=-1 \hspace{20pt} &(2) \end{cases}$$ Multiplying equation $(1)$ by $2$ so that the coefficients of $y$ in the two equations are additive inverses gives: $x+\dfrac{2}{3}y=6\hspace{20pt} (1)$ $\text{Add the two equations to eliminate } y:$ \[ \begin{aligned} x+\dfrac{2}{3}y&=6 \\[2mm] \dfrac{1}{4}x-\dfrac{2}{3}y&=-1 \ \\[3mm] \hline \dfrac{5}{4}x&=5\\[2mm] \end{aligned} \] Multiply both sides by $\dfrac{4}{5}$ to obtain: \begin{align*} \frac{4}{5} \cdot \frac{5}{4}x&=5\cdot \frac{4}{5}\\\\ x&=4 \end{align*} $\text{Substituting in equation (1) for }x=4$ gives: $\dfrac{1}{2} (4)+\dfrac{1}{3}y=3$ $2+\dfrac{1}{3}y =3$ $\dfrac{1}{3}y=1$ $y = 3$ Therefore, the solution is: $\boxed{x=4 \hspace{20pt} y = 3}$
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