Maths 問題~~~?

3cos^2x-5sinx-1=0
3(1-sin^2 x)-5sinx-1=0
-sin^2 x-5sin x-4=0
sinx=-1 or sinx=-4 (Delete)
x=270

3(1-sin^2 x)-5 sinx - 1 = 0
3-3 sin^2 x - 5 sinx - 1 = 0
-3 sin^2 x - 5 sinx +2 =0
sin x = -2 (rej) or sin x = 1/3
so , x = 19.5 or 161