Maths problem： how to do, thanks. I am not sure my answer.?

(5 cos x - 1)(sin x + 1) = 0
iff. cos x = 1/5 or sin x = -1
cos x = 1/5, two solutions
sin x = -1, one solution.

我懂計算這條題目了,,謝謝大家,請協助我另一题吧