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: 15

Answer

1. The curve ${{\bf{r}}_1}\left( t \right) = \left( {t,{t^2}} \right)$. The tangent vector at $t=1$ is ${{\bf{r}}_1}'\left( 1 \right) = \left( {1,2} \right)$. The point corresponding to $t=1$ is ${{\bf{r}}_1}\left( 1 \right) = \left( {1,1} \right)$. 2. The curve ${{\bf{r}}_2}\left( t \right) = \left( {{t^3},{t^6}} \right)$. The tangent vector at $t=1$ is ${{\bf{r}}_2}'\left( 1 \right) = \left( {3,6} \right)$. The point corresponding to $t=1$ is ${{\bf{r}}_2}\left( 1 \right) = \left( {1,1} \right)$. Please see the figure attached. The red arrow represents the tangent vector.

Work Step by Step

1. The curve ${{\bf{r}}_1}\left( t \right) = \left( {t,{t^2}} \right)$. We get ${{\bf{r}}_1}'\left( t \right) = \left( {1,2t} \right)$. Thus, the tangent vector at $t=1$ is ${{\bf{r}}_1}'\left( 1 \right) = \left( {1,2} \right)$. The point corresponding to $t=1$ is ${{\bf{r}}_1}\left( 1 \right) = \left( {1,1} \right)$. 2. The curve ${{\bf{r}}_2}\left( t \right) = \left( {{t^3},{t^6}} \right)$. We get ${{\bf{r}}_2}'\left( t \right) = \left( {3{t^2},6{t^5}} \right)$. Thus, the tangent vector at $t=1$ is ${{\bf{r}}_2}'\left( 1 \right) = \left( {3,6} \right)$. The point corresponding to $t=1$ is ${{\bf{r}}_2}\left( 1 \right) = \left( {1,1} \right)$. 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 curves. $\begin{array}{*{20}{c}} t&{{{\bf{r}}_1}\left( t \right) = \left( {x,y} \right)}\\ { - 3}&{\left( { - 3,9} \right)}\\ { - 2}&{\left( { - 2,4} \right)}\\ { - 1}&{\left( { - 1,1} \right)}\\ 0&{\left( {0,0} \right)}\\ 1&{\left( {1,1} \right)}\\ 2&{\left( {2,4} \right)}\\ 3&{\left( {3,9} \right)} \end{array}\begin{array}{*{20}{c}} {}&{} \end{array} \begin{array}{*{20}{c}} t&{{{\bf{r}}_2}\left( t \right) = \left( {x,y} \right)}\\ { - 3}&{\left( { - 27,729} \right)}\\ { - 2}&{\left( { - 8,64} \right)}\\ { - 1}&{\left( { - 1,1} \right)}\\ 0&{\left( {0,0} \right)}\\ 1&{\left( {1,1} \right)}\\ 2&{\left( {8,64} \right)}\\ 3&{\left( {27,729} \right)} \end{array}$
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