Find the domain of the vector functions, r(t), listed below.
You may use \"-INF\" for $-\infty$ and use \"INF\" for $\infty$ as necessary, and use \"U\" for a union symbol if a union of intervals
is needed.
a) r(t) = $\langle \ln(11t), \sqrt{t+8}, \frac{1}{\sqrt{13-t}} \rangle$
(0,13)
b) r(t) = $\langle \sqrt{t-4}, \sin(6t), t^2 \rangle$
$(-\infty, 4)$