The question provides an explicit function formula and asks to find critical points (where f'=0) and determine whether each is a local minimum, local maximum, or neither, using derivative tests.
| (A) | The point $x = 0$ is a point of local maxima of $f$ |
| (B) | The point $x = 0$ is a point of local minima of $f$ |
| (C) | Number of points of local maxima of $f$ in the interval $[ \pi , 6 \pi ]$ is 3 |
| (D) | Number of points of local minima of $f$ in the interval $[ 2 \pi , 4 \pi ]$ is 1 |