Question

Find the x-coordinates of all points on the
graph of f(x) = 6 sin x + (sinx)^2 at which the tangent line is horizontal...Here are the answers:
1. π/3+ nπ, all integers n
2. π/4+ 2nπ, all integers n
3.π/4+ nπ, all integers n
4. π/2+ 2nπ, all integers n
5. π/3+ 2nπ, all integers n
6. π/2+ nπ, all integers n

Answer 1

4.
Refer to the attachment