Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 3 - Polynomial and Rational Functions - 3.6 Variation - 3.6 Exercises - Page 387: 7


When $x=-6$, the value of $y$ is $-30$.

Work Step by Step

$y$ varies directly so its equation is of the form $y=kx$. When $y=20$, $x=4$. Substitute these values into $y=kx$ to obtain: $y=kx \\20=k(4) \\\frac{20}{4}=\frac{k(4)}{4} \\5=k$ Thus, the direct variation is $y=5x$. To find the value of $y$ when $x=-6$, substitute $-6$ to $x$ in the equation above to obtain: $y=5x \\y=5(-6) \\y=-30$
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