Y = cos square x-sin square x + 3sinx Find the maximum and minimum

Y = cos square x-sin square x + 3sinx Find the maximum and minimum

∵cos²x=1-sin²x
∴y=1-2sin²x+3sinx
Let SiNx = X,
y=-2x²+3x+1=-2(x-3/4)²+9/8
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