Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 10 - Section 10.2 - Calculus with Parametric Curves - 10.2 Exercises - Page 680: 34

Answer

Only $y=x-1$

Work Step by Step

Eliminate the parameter $t$: $x=3t^2+1$ and $y=2t^3+1$ $x-1=3t^2$ and $y-1=2t^3$ $(x-1)^3=27t^6$ and $(y-1)^2=4t^6$ $\frac{(x-1)^3}{27}=t^6$ and $\frac{(y-1)^2}{4}=t^6$ (Substract both) $\frac{(x-1)^3}{27}-\frac{(y-1)^2}{4}=0$ Take the implicit differentiation to find the slope of the tangent at $(4,3)$: $\frac{(x-1)^2}{9}-\frac{y-1}{2}\frac{dy}{dx}=0$ $\frac{dy}{dx}=\frac{2(x-1)^2}{9(y-1)}$ $m=\frac{dy}{dx}|_{(4,3)}$ $m=\frac{2(4-1)^2}{9(3-1)}$ $m=\frac{18}{18}$ $m=1$ Find the equation of the tangent: $y-3=m(x-4)$ $y-3=1(x-4)$ $y-3=x-4$ $y=x-1$ Thus, the equation of the tangents to the curve are only $y=x-1$.
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