Which of the following is equal to the area of the region inside the polar curve r=2cos(θ) and outside the polar curve r=cos(θ)?

a) 3 ∫ cos^2 (θ) dθ from 0 to pi/2

b) 3 ∫ cos^2 (θ) dθ from 0 to pi

c) (3/2) ∫ cos^2 (θ) dθ from 0 to pi/2

d) 3 ∫ cos(θ) dθ from 0 to pi/2

e) 3 ∫ cos(θ) dθ from 0 to pi

I worked through the problem and got ∫ 3*cos^2 (θ) dθ from 0 to pi. The answer in my textbook says is A. But I don't know why the answer isn't B. Can anyone tell me how to simplify to get answer A?

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