passpadi

2006

Mathematics

JAMB

Differentiate (cos θ - sin θ)2

A.

-2 cos 2θ

B.

-2 sin2θ

C.

1 - 2 cos 2θ

D.

1 - 2 sin 2θ

Correct Answer: -2 cos 2θ

Explanation

y = (cosθ - sinθ) dy/dx = 2(cosθ - sinθ)(-sinθ - cosθ) dy/dx = 2(-cosθsinθ - cos2θ + sin2θ) dy/dx = 2(- cos2θ + sin2θ) = -2(cos2θ - sin2θ) = -2(1 - sin2θ) = -2cos2θ

y = (cosθ - sinθ) dy/dx = 2(cosθ - sinθ)(-sinθ - cosθ) dy/dx = 2(-cosθsinθ - cos2θ + sin2θ) dy/dx = 2(- cos2θ + sin2θ) = -2(cos2θ - sin2θ) = -2(1 - sin2θ) = -2cos2θ
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