Solve `cos 4 theta+ sin 5 theta=2`.

Explanation

The equation `cos 4theta+ sin 5 theta=2` is valid only when `cos 4 theta=1` and `sin 5 theta=1`. Thus,
`4 theta=2npi and 5 theta=2m pi+pi//2, n , m in Z`
`rArr theta=(2n pi)/4 and theta=(2m pi)/5+pi/10, n, m in Z`
Putting n, `m=0, pm 1, pm 2`, ..., the common value in `[0, 2pi]` is `theta=pi//2`. Therefore, the solution is `theta=2k pi+pi//2, k in Z`.