Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 3: Derivatives - Section 3.2 - The Derivative as a Function - Exercises 3.2 - Page 117: 53

Answer

Yes, $y=-x-13$ at $(3,-16)$.

Work Step by Step

Step 1. Given $y=f(x)=2x^2-13x+5$, we have $y'=f'(x)=\lim_{h\to0}\frac{f(x+h)-f(x)}{h}=\lim_{h\to0}\frac{2(x+h)^2-13(x+h)+5-2x^2+13x-5}{h}=\lim_{h\to0}\frac{4xh+2h^2-13h}{h}=\lim_{h\to0}(4x+2h-13)=4x-13$ Step 2. Let $y'=-1$; we have $4x-13=-1$, which gives $x=3$ Step 3. The point on the curve with $x=3$ is $y=2(3)^2-13(3)+5=-16$, or $(3,-16)$ Step 4. With the slope $m=-1$, the tangent line equation can be written as $y+16=-1(x-3)$ which gives $y=-x-13$ at the point of tangency of $(3,-16)$.
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