Thomas' Calculus 13th Edition

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

Chapter 3: Derivatives - Section 3.1 - Tangents and the Derivative at a Point - Exercises 3.1 - Page 109: 50

Answer

(x,y)= (-1,-5/6) and (4,-5/3)

Work Step by Step

Rearrange the equation 8x-2y=1 become: 8x-1=2y 2y=8x-1 y=(8x/2)-(1/2) y=4x-1/2. From y=mx+c, we know m=4. Differentiate g(x)=(1/3)x^{3} - (3/2)x^{2} + 1 dg/dx= (1/3)(3)x^{3-1} - (3/2)(2)x^{2-1} +0 dg/dx= x^{2} - 6x The tangent line is parallel to the line 8x-2y=1, thus slope of the tangent line = 4. So, x^{2} - 6x = 4. x^{2} - 6x -4 =0 Factorize the equation. (x-4)(x+1)=0 so we get x-4=0 and x+1=0. The first point is when x-4=0, x=4. To find y-coordinate, we substitute x with 4 in the g(x). So, g(4)=(1/3)(4)^{3} - (3/2)(4)^{2} + 1 g(4)=-5/3. The second point is when x+1=0, x=-1, Same as above, substitute x with -1 in g(x), g(-1)=(1/3)(-1)^{3} - (3/2)(-1)^{2} + 1 g(-1)=-5/6 Therefore, (x,y)= (-1,-5/6) and (4,-5/3).
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