Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 14 - Calculus of Vector-Valued Functions - 14.4 Curvature - Exercises - Page 735: 29

Answer

The curvature at $t=2$ is $\kappa \left( 2 \right) \simeq 0.012$

Work Step by Step

We have $\left( {x\left( t \right),y\left( t \right)} \right) = \left( {{t^2},{t^3}} \right)$. The derivatives are $\left( {x'\left( t \right),y'\left( t \right)} \right) = \left( {2t,3{t^2}} \right)$ $\left( {x{\rm{''}}\left( t \right),y{\rm{''}}\left( t \right)} \right) = \left( {2,6t} \right)$ Using Eq. (11) we compute the curvature $\kappa \left( t \right) = \frac{{\left| {x'\left( t \right)y{\rm{''}}\left( t \right) - x{\rm{''}}\left( t \right)y'\left( t \right)} \right|}}{{{{\left( {x'{{\left( t \right)}^2} + y'{{\left( t \right)}^2}} \right)}^{3/2}}}}$ $\kappa \left( t \right) = \frac{{\left| {12{t^2} - 6{t^2}} \right|}}{{{{\left( {4{t^2} + 9{t^4}} \right)}^{3/2}}}} = \frac{{6{t^2}}}{{{{\left( {4{t^2} + 9{t^4}} \right)}^{3/2}}}}$ The curvature at $t=2$ is $\kappa \left( 2 \right) = \frac{{6\cdot4}}{{{{\left( {4\cdot4 + 9\cdot16} \right)}^{3/2}}}} = \frac{3}{{80\sqrt {10} }} \simeq 0.012$
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