Answer
(a) $\frac{3\sqrt {10}}{10}$
(b) $\frac{\sqrt {10}}{10}$
(c) $\frac{1}{3}$
Work Step by Step
(a) $cos\frac{\alpha}{2}=\sqrt {\frac{1+cos\alpha}{2}}=\sqrt {\frac{1+4/5}{2}}=\frac{3\sqrt {10}}{10}$
(b) $sin\frac{\alpha}{2}=\sqrt {\frac{1-cos\alpha}{2}}=\sqrt {\frac{1-4/5}{2}}=\frac{\sqrt {10}}{10}$
(c) $tan\frac{\alpha}{2}=\frac{1-cos\alpha}{sin\alpha}=\frac{1-4/5}{3/5}=\frac{1}{3}$
