Calculus: Early Transcendentals (2nd Edition)

Published by Pearson
ISBN 10: 0321947347
ISBN 13: 978-0-32194-734-5

Chapter 3 - Derivatives - 3.8 Implicit Differentiation - 3.8 Exercises - Page 202: 83

Answer

$$\frac{{dy}}{{dx}} = \frac{{7{y^2} - 3{x^2} - 4x{y^2} - 4{x^3}}}{{2y\left( {2{x^2} + 2{y^2} - 7x} \right)}}$$

Work Step by Step

$$\eqalign{ & \left( {{x^2} + {y^2}} \right)\left( {{x^2} + {y^2} + x} \right) = 8x{y^2} \cr & {\text{Distributive property}} \cr & {x^4} + {x^2}{y^2} + {x^3} + {x^2}{y^2} + {y^4} + x{y^2} = 8x{y^2} \cr & {x^4} + 2{x^2}{y^2} + {x^3} + {y^4} + x{y^2} = 8x{y^2} \cr & {x^4} + 2{x^2}{y^2} + {x^3} + {y^4} - 7x{y^2} = 0 \cr & {\text{Differentiate both sides with respect to }}x \cr & 4{x^3} + 4{x^2}yy' + 4x{y^2} + 3{x^2} + 4{y^3}y' - 14xyy' - 7{y^2} = 0 \cr & {\text{Collect like terms}} \cr & 4{x^2}yy' + 4{y^3}y' - 14xyy' = 7{y^2} - 3{x^2} - 4x{y^2} - 4{x^3} \cr & \left( {4{x^2}yy' + 4{y^3}y' - 14xyy'} \right) = 7{y^2} - 3{x^2} - 4x{y^2} - 4{x^3} \cr & \left( {4{x^2}y + 4{y^3} - 14xy} \right)y' = 7{y^2} - 3{x^2} - 4x{y^2} - 4{x^3} \cr & {\text{Solve for }}y' \cr & \frac{{dy}}{{dx}} = \frac{{7{y^2} - 3{x^2} - 4x{y^2} - 4{x^3}}}{{4{x^2}y + 4{y^3} - 14xy}} \cr & \frac{{dy}}{{dx}} = \frac{{7{y^2} - 3{x^2} - 4x{y^2} - 4{x^3}}}{{2y\left( {2{x^2} + 2{y^2} - 7x} \right)}} \cr} $$
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