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Evaluate sin²(72deg) - sin²(60deg).

1. (sqrt(5) - 1)/8
2. (1 + sqrt(5))/8
3. (3 + sqrt(5))/16
4. (sqrt(5) - 1)/16

Correct answer: (sqrt(5) - 1)/8

Solution

The expression equals sin(132deg)sin(12deg); evaluating numerically gives 0.1545 = (sqrt5 - 1)/8.

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