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# When a tangent line is horizontal?

Find all points on the graph of the function f(x) = 2sinx + sin²x at which the tangent line is horizontal.

I need help. I am stuck.

### 1 Answer

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- ComoLv 71 month ago
f ' (x) = 2 cos x + 2 sin x cos x = 0

2 cos x ( 1 + sin x ) = 0

cos x = 0 , sin x = -1/2

x = π/2 , 3π/2 , x = 7π/6 , 11π/6_________ ± 2n π

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Wouldn't sin(x) = -1