Algebra: A Combined Approach (4th Edition)

Published by Pearson
ISBN 10: 0321726391
ISBN 13: 978-0-32172-639-1

Chapter 4 - Test - Page 331: 18

Answer

$$x=\frac{47}{5}$$ $$y=\frac{48}{5}$$

Work Step by Step

Equation 1: $x-\frac{2}{3}y=3$ Equation 2: $-2x + 3y = 10$ Multiply equation 1 by $2$: $$[x-\frac{2}{3}y=3]\cdot2$$ $$2x-\frac{4}{3}y=6$$ We can call this equation 1'. Add equation 1' to equation 2: $$2x-\frac{4}{3}y=6$$ $$+$$ $$-2x + 3y = 10$$ $$=$$ $$\frac{5}{3}y=16$$ Multiply the whole equation by $3$: $$[\frac{5}{3}y=16]\cdot3$$ $$5y=48$$ Divide both sides by $5$: $$\frac{5y}{5}=\frac{48}{5}$$ $$y=\frac{48}{5}$$ Substitute this value of $y$ to equation 2: $$-2x + 3y = 10$$ $$-2x + 3(\frac{48}{5}) = 10$$ $$-2x + \frac{144}{5} = 10$$ Subtract $\frac{144}{5}$ from both sides: $$-2x + \frac{144}{5} -\frac{144}{5}= 10-\frac{144}{5}$$ $$-2x =\frac{50}{5}-\frac{144}{5}$$ $$-2x =-\frac{94}{5}$$ Divide both sides by $-2$: $$\frac{-2x}{-2} =\frac{-\frac{94}{5}}{-2}$$ $$x=-\frac{94}{5}\cdot-\frac{1}{2}$$ $$x=\frac{94}{10}$$ $$x=\frac{47}{5}$$ Check using equation 1: $$x-\frac{2}{3}y=3$$ $$\frac{47}{5}-\frac{2}{3}(\frac{48}{5})=3$$ $$\frac{47}{5}-\frac{96}{15}=3$$ $$\frac{141}{15}-\frac{96}{15}=3$$ $$\frac{45}{15}=3$$ $$3=3$$
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