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If cos A = 3/4, find the value of 32 sin(A/2) sin(5A/2).

1. 11
2. -11
3. 12
4. 4

Correct answer: 11

Solution

Converting to a difference of cosines and using cos(2A) and cos(3A) in terms of cosA = 3/4 gives the value 11.

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