Answer
(a) maximum at $(\displaystyle \frac{\pi}{2}, 1)$
(b) minimum at $(-\displaystyle \frac{\pi}{2},-1)$
Work Step by Step
(a) We see from the graph that $f$ has a local maximum at $(\displaystyle \frac{\pi}{2}, 1)$
(b) We see from the graph that $f$ has a local minimum at $(-\displaystyle \frac{\pi}{2},-1)$