Algebra and Trigonometry 10th Edition

Published by Cengage Learning
ISBN 10: 9781337271172
ISBN 13: 978-1-33727-117-2

Chapter 1 - 1.4 - Quadratic Equations and Applications - 1.4 Exercises - Page 112: 116b

Answer

Verifying algebraically, the year is $2007$.

Work Step by Step

Verifying algebraically: $$P=-0.0038t^2+0.272t+5.25$$ Substituting $P=7$ into the equation: $$7=-0.0038t^2+0.272t+5.25$$ $$-0.0038t^2+0.272t-1.75$$ Using the quadratic formula: $$t=\frac{-0.272\pm\sqrt{0.272^2-4(-0.0038)(-1.75)}}{2(-0.0038)}$$ $$t_1=\frac{-0.272+\sqrt{0.272^2-4(-0.0038)(-1.75)}}{2(-0.0038)}=7.15$$ $$t_2=\frac{-0.272-\sqrt{0.272^2-4(-0.0038)(-1.75)}}{2(-0.0038)}=64.43$$ Based on the constraint of $1\leq t\leq14$, take $t=7.15\approx7$. Then, the year is: $$Year=2000+7=2007$$
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