Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 12 - Vector-Valued Functions - 12.5 Curvature - Exercises Set 12.5 - Page 880: 52

Answer

(a) $\quad\left(0, \frac{-5}{2}\right), \left(\frac{5}{3}, 0\right) $ (b) Clockwise (c) Point

Work Step by Step

Since \[ \begin{array}{ll} -3 \sin t=x^{\prime}, & -3 \cos t=x^{\prime \prime} \\ 2 \cos t=y^{\prime}, & -2 \sin t=y^{\prime \prime} \end{array} \] We use the formulas to calculate the coordinates of the center of curvature $(\zeta, \eta)$ : \[ \begin{aligned} \ &-y^{\prime} \frac{\left(y^{\prime}\right)^{2}+\left(x^{\prime}\right)^{2}}{x^{\prime} y^{\prime \prime}-x^{\prime \prime} y^{\prime}}+x=zeta \\ &-2 \cos t \frac{4 \cos ^{2} t+9 \sin ^{2} t}{6}+3 \cos t = \zeta \\ \frac{5}{3}=\zeta(0) & \end{aligned} \] So \[ x^{\prime} \frac{\left(x^{\prime}\right)^{2}+\left(y^{\prime}\right)^{2}}{x^{\prime} y^{\prime \prime}-x^{\prime \prime} y^{\prime}}+y=\eta \] \[ \begin{aligned} \eta &=2 \sin t-3 \sin t \frac{9 \sin ^{2} t+4 \cos ^{2} t}{6} \\ \eta(0) &=0 \end{aligned} \] The center of curvature is $\left(\frac{5}{3}, 0\right)$ \[ \begin{array}{l} 0=\zeta(\pi / 2) \\ \frac{-5}{2}=\eta(\pi / 2) \end{array} \] And then $\left(0, \frac{-5}{2}\right)$ The direction of the evolute that is tracked while increasing $t$ from 0 to $2\pi$ is tracked clockwise. The evolution of a circle is a point, which is the center of the circle.
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