Calculus with Applications (10th Edition)

Published by Pearson
ISBN 10: 0321749006
ISBN 13: 978-0-32174-900-0

Chapter 7 - Integration - 7.5 The Area Between Two Curves - 7.5 Exercises - Page 405: 17

Answer

$$A = \frac{1}{2}$$

Work Step by Step

$$\eqalign{ & y = {x^3} - {x^2} + x + 1,\,\,\,\,y = 2{x^2} - x + 1 \cr & {\text{Find the points of intersection of the graphs}} \cr & {x^3} - {x^2} + x + 1 = 2{x^2} - x + 1 \cr & {x^3} - {x^2} + x + 1 - 2{x^2} + x - 1 = 0 \cr & {x^3} - 3{x^2} + 2x = 0 \cr & x\left( {{x^2} - 3x + 2} \right) = 0 \cr & x\left( {x - 1} \right)\left( {x - 2} \right) = 0 \cr & x = 0,x = 1,x = 2 \cr & {\text{Then with the critical values we have the intervals }}\left( {0,1} \right){\text{ and }}\left( {1,2} \right) \cr & {\text{For the interval }}\left( {0,1} \right){\text{ we have that }}{x^3} - {x^2} + x + 1 > 2{x^2} - x + 1 \cr & {\text{and }} \cr & {\text{For the interval }}\left( {1,2} \right){\text{ we have that }}2{x^2} - x + 1 > {x^3} - {x^2} + x + 1 \cr & \cr & {\text{The area is given by}}: \cr & A = \int_0^1 {\left( {{x^3} - {x^2} + x + 1 - 2{x^2} + x - 1} \right)} dx + \int_1^2 {\left( {2{x^2} - x + 1 - {x^3} + {x^2} - x - 1} \right)} dx \cr & A = \int_0^1 {\left( {{x^3} - 3{x^2} + 2x} \right)} dx + \int_1^2 {\left( {3{x^2} - 2x - {x^3}} \right)} dx \cr & {\text{Integrating}} \cr & A = \left( {\frac{1}{4}{x^4} - {x^3} + {x^2}} \right)_0^1 + \left( {{x^3} - {x^2} - \frac{1}{4}{x^4}} \right)_1^2 \cr & A = \left( {\frac{1}{4}{{\left( 1 \right)}^4} - {{\left( 1 \right)}^3} + {{\left( 1 \right)}^2}} \right) - \left( {\frac{1}{4}{{\left( 0 \right)}^4} - {{\left( 0 \right)}^3} + {{\left( 0 \right)}^2}} \right) + \left( {{{\left( 2 \right)}^3} - {{\left( 2 \right)}^2} - \frac{1}{4}{{\left( 2 \right)}^4}} \right) \cr & - \left( {{{\left( 1 \right)}^3} - {{\left( 1 \right)}^2} - \frac{1}{4}{{\left( 1 \right)}^4}} \right) \cr & \cr & A = \left( {\frac{1}{4}} \right) - \left( 0 \right) + \left( 0 \right) - \left( { - \frac{1}{4}} \right) \cr & A = \frac{1}{2} \cr} $$
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