Answer
(a) $ \frac{1}{4}$
(b) $ \frac{3}{4}$
Work Step by Step
Given $f(\theta)=cos\theta$ (an even function) with $f(a)=cos(a)=\frac{1}{4}$, we have:
(a) $f(-a)=f(a)=\frac{1}{4}$.
(b) $f(a)+f(a+2\pi)+f(a-2\pi)=cos(a)+cos(a+2\pi)+cos(-2\pi+a)=3cos(a)=\frac{3}{4}$
