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In a triangle ABC, sin A - cos B = cos C, with angle B greater than angle C. Find angle B.

1. pi/2
2. pi/3
3. pi/4
4. pi/6

Correct answer: pi/2

Solution

Substituting sin A = sin(B+C) and using sum-to-product leads to a factor giving cos(B/2...); solving with B > C yields B = pi/2.

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