Math question: What is the 3rd derivative of f(x) = cos(2x) at x = π/4?
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What is the variance of the numbers 4, 7, 9, 12, 15?
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Question: In a triangle ABC, the angle bisector of angle B divides the side AC into segments AB = 6 cm and BC = 9 cm. What is the length of the angle bisector?