Thomas' Calculus 13th Edition

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

Chapter 8: Techniques of Integration - Practice Exercises - Page 517: 17

Answer

$$ - \frac{3}{8}\ln \left| v \right| + \frac{1}{{16}}\ln \left| {v + 2} \right| + \frac{5}{{16}}\ln \left| {v - 2} \right| + C$$

Work Step by Step

$$\eqalign{ & \int {\frac{{v + 3}}{{2{v^3} - 8v}}} dv \cr & {\text{Decompose the integrand into partial fractions.}} \cr & {\text{The form of the partial fraction decomposition is}} \cr & \frac{{v + 3}}{{2{v^3} - 8v}} = \frac{{v + 3}}{{2v\left( {{v^2} - 4} \right)}} = \frac{{v + 3}}{{2v\left( {v + 2} \right)\left( {v - 2} \right)}} \cr & \frac{{v + 3}}{{2v\left( {v + 2} \right)\left( {v - 2} \right)}} = \frac{A}{{2v}} + \frac{B}{{v + 2}} + \frac{C}{{v - 2}} \cr & \cr & {\text{Multiplying by }}2v\left( {v + 2} \right)\left( {v - 2} \right){\text{, we have}} \cr & v + 3 = A\left( {v + 2} \right)\left( {v - 2} \right) + 2Bv\left( {v - 2} \right) + 2Cv\left( {v + 2} \right)\,\,\,\,\,\left( {\bf{1}} \right) \cr & \cr & {\text{if we set }}v = 0{\text{ into equation }}\left( {\bf{1}} \right) \cr & 0 + 3 = A\left( 2 \right)\left( { - 2} \right) + B\left( 0 \right) + C\left( 0 \right) \cr & A = - \frac{3}{4} \cr & \cr & {\text{if we set }}v = - 2{\text{ into equation }}\left( {\bf{1}} \right) \cr & - 2 + 3 = A\left( 0 \right) + 2B\left( { - 2} \right)\left( { - 4} \right) + C\left( 0 \right) \cr & B = \frac{1}{{16}} \cr & \cr & {\text{if we set }}v = 2{\text{ into equation }}\left( {\bf{1}} \right) \cr & 2 + 3 = A\left( 0 \right) + 2B\left( 0 \right) + 2C\left( 2 \right)\left( {2 + 2} \right) \cr & C = \frac{5}{{16}} \cr & \cr & {\text{The decomposition of the integrand is}} \cr & \frac{{v + 3}}{{2v\left( {v + 2} \right)\left( {v - 2} \right)}} = \frac{{ - 3/4}}{{2v}} + \frac{{1/16}}{{v + 2}} + \frac{{5/16}}{{v - 2}} \cr & \cr & \int {\frac{{v + 3}}{{2{v^3} - 8v}}} dv = - \frac{3}{8}\int {\frac{1}{v}dv + \frac{1}{{16}}\int {\frac{1}{{v + 2}}dv} + \frac{5}{{16}}\int {\frac{1}{{v - 2}}} dv} \cr & {\text{Integrating, we get}} \cr & = - \frac{3}{8}\ln \left| v \right| + \frac{1}{{16}}\ln \left| {v + 2} \right| + \frac{5}{{16}}\ln \left| {v - 2} \right| + C \cr} $$
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