Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 3 - Differentiation - 3.5 Higher Derivatives - Exercises - Page 135: 16

Answer

$$ y''=-\frac{1}{4}r^{-3/2}-\frac{3}{4}r^{-1/2}-2, \quad y'''=\frac{3}{8}r^{-5/2}+\frac{3}{8}r^{-3/2}.$$

Work Step by Step

Let $ y=(r^{1/2}+r)(1-r)$; simplify $ y $ as follows $$ y=r^{1/2}+r-r^{3/2}-r^2.$$ Now, we get $$ y'=\frac{1}{2}r^{-1/2}+1-\frac{3}{2}r^{1/2}-2r.$$ $$ y''=-\frac{1}{4}r^{-3/2}-\frac{3}{4}r^{-1/2}-2, \quad y'''=\frac{3}{8}r^{-5/2}+\frac{3}{8}r^{-3/2}.$$
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