Chapter 11 - Vectors and Vector-Valued Functions - 11.6 Calculus of Vector-Valued Functions - 11.6 Exercises - Page 815: 18

$\textbf{r}'(\pi) = \langle -2, 0, 0\rangle$

$\textbf{r}(t) = \langle f(t), g(t), h(t)\rangle$ $\textbf{r}'(t) = \langle f'(t), g'(t), h'(t)\rangle$ $\textbf{r}(t) = \langle 2sin(t),3cos(t),sin(t/2)\rangle$ $\textbf{r}'(t) = \langle 2cos(t), -3sin(t), 0.5cos(t/2)\rangle$ $\textbf{r}'(\pi) = \langle 2cos(\pi), -3sin(\pi), 0.5cos(\pi/2\rangle = \langle -2, 0, 0\rangle$