Answer
$-\frac{\sqrt {15}}{7}$
Work Step by Step
1. Use the given figures, we have $cos\alpha=-\frac{1}{4}, sin\alpha=-\frac{\sqrt {15}}{4},tan\alpha=\sqrt {15}$
2. $h(2\alpha)=tan(2\alpha)=\frac{2tan\alpha}{1-tan^2\alpha}=\frac{2\sqrt {15}}{1-15}=-\frac{\sqrt {15}}{7}$
