Answer
$\frac{\sqrt {10}}{4}$
Work Step by Step
Step 1. Using the given figures, we have $a=-\sqrt {5-4}=-1, b=-\sqrt {1-\frac{1}{16}}=-\frac{\sqrt {15}}{4}$
Step 2. $f(\frac{\alpha}{2})=sin(\frac{\alpha}{2})=\sqrt {\frac{1-cos\alpha}{2}}=\sqrt {\frac{1-(-1/4)}{2}}=\frac{\sqrt {10}}{4}$
