Let

- Find all points such that ;
- Determine the intervals on which is monotonic by examining the sign of ;
- Determine the intervals on which is monotonic by examining the sign of ;
- Sketch the graph of .

- We take the derivative,
Thus,

for an integer. (We found the zeros of sine in this exercise, Apostol Section 2.8 Exercise #1.)

- is increasing if and decreasing if .
- Taking the second derivative,
Thus, is increasing if and decreasing if .

- We sketch the curve,

Second derivative should be 2cos2x (not -2cos2x). The rest of the answer is correct.