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 - Chapter 12 Review Exercises - Page 903: 22

Answer

\begin{array}{l} T(0)=\frac{1}{\sqrt{5}} j-\frac{2}{\sqrt{5}} k \\ N(0) \frac{-2}{3} i-\frac{2}{3} j-\frac{1}{3} k \\ B(0)=\left\langle-\frac{\sqrt{5}}{3}, \frac{4 \sqrt{5}}{15}, \frac{2 \sqrt{5}}{15}\right\rangle \end{array}

Work Step by Step

We find: \[ \mathbf{r}(t)=\left\langle 2 \cos t, 2 \cos t+\frac{3}{\sqrt{5}} \sin t, \cos t-\frac{6}{\sqrt{5}} \sin t\right\rangle \] \[ \begin{array}{l} \left\langle-2 \sin t,-2 \sin t+\frac{3}{\sqrt{5}} \cos t,-\sin t-\frac{6}{\sqrt{5}} \cos t\right\rangle=\mathrm{r}^{\prime}(t) \\ \left\langle-2 \cos t,-2 \cos t-\frac{3}{\sqrt{5}} \sin t,-\cos t+\frac{6}{\sqrt{5}} \sin t\right\rangle =\mathrm{r}^{\prime \prime}(t)\\ \qquad \begin{aligned} \mathrm{T}(0)=& \frac{\mathrm{r}^{\prime}(0)}{\left\|\mathrm{r}^{\prime}(0)\right\|} \\ =& \frac{(0) \mathrm{i}+(3 / \sqrt{5}) \mathrm{j}-(6 / \sqrt{5}) \mathrm{k}}{\sqrt{(9 / 5)+(36) / 5}} \\ =& \frac{1}{\sqrt{5}} \mathrm{j}-\frac{2}{\sqrt{5}} \mathrm{k} \\ =& \frac{\mathrm{r}^{\prime \prime}(0)}{\left\|\mathrm{r}^{\prime \prime}(0)\right\|} \\ =& \frac{-2 \mathrm{i}-2 \mathrm{j}-\mathrm{k}}{\sqrt{4+4+1}} \\ =& \frac{-2}{3} \mathrm{i}-\frac{2}{3} \mathrm{j}-\frac{1}{3} \mathrm{k} \end{aligned} \\ \begin{aligned} \mathrm{B}(0)=\mathrm{T}(0) \times \mathrm{N}(0) & \\ =\frac{1}{3 \sqrt{5}}\left|\begin{array}{rrr} \mathrm{N} & 1 & \mathrm{j} \\ 1 & -2 & 1 \\ -2 & -2 & -1 \end{array}\right| \\ =&\left\langle-\frac{\sqrt{5}}{3}, \frac{4 \sqrt{5}}{15}, \frac{2 \sqrt{5}}{15}\right\rangle \end{aligned} \end{array} \]
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