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 - 14.2 Calculus of Vector-Valued Functions - Exercises - Page 720: 14

Answer

The tangent vector at $t=1$ is ${\rm{r}}'\left( 1 \right) = \left( { - 2,1} \right)$ Please see the figure attached. The red arrow represents the tangent vector.

Work Step by Step

Recall that the derivative vector ${\rm{r}}'\left( {{t_0}} \right)$ points in the direction tangent to the path traced by ${\bf{r}}\left( t \right)$ at $t = {t_0}$. For the curve ${\bf{r}}\left( t \right) = \left( {1 - {t^2},t} \right)$ we get ${\rm{r}}'\left( t \right) = \left( { - 2t,1} \right)$. Thus, the tangent vector at $t=1$ is ${\rm{r}}'\left( 1 \right) = \left( { - 2,1} \right)$. The point corresponding to $t=1$ is ${\bf{r}}\left( 1 \right) = \left( {0,1} \right)$. We evaluate several points for the interval $ - 3 \le t \le 3$ and list them in the following table. Then we plot the points and join them to obtain the curve. $\begin{array}{*{20}{c}} t&{\left( {x,y} \right)}\\ { - 3}&{\left( { - 8, - 3} \right)}\\ { - 2}&{\left( { - 3, - 2} \right)}\\ { - 1}&{\left( {0, - 1} \right)}\\ 0&{\left( {1,0} \right)}\\ 1&{\left( {0,1} \right)}\\ 2&{\left( { - 3,2} \right)}\\ 3&{\left( { - 8,3} \right)} \end{array}$
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