When does cosx times sinx times sinx equal 1?

CosX(Sin^(2)X) = 1

Use trig. identity ; Sin^(X) =

(1 - Cos^(2)X)

Hence

CosX(1 - Cos^(2)(X)) = 1

CosX = 1

X = 0

&

1 - Cos^(2)x = 1

Cos^(2)X = 0 ( 1 - 1)

Square rooting

CosX = 0

X = 90, 270 ....