trigon. problem(M2)....20分!!!!

2011-10-31 5:10 pm

It is given that sin A+cos A=3/2, find the value of sin(2A).

Formulas that can uses: Compound angle formulas, Double angle formulas, Product to sum formulas, sum to product formulas.

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回答 (1)

用戶10012

2011-10-31 5:18 pm

✔ 最佳答案

sin A + cos A = 3/2
(sin A + cos A)^2 = (3/2)^2
sin^2 A + 2 sin A cos A + cos^2 A = 9/4
1 + 2 sin A cos A = 2.25
so 2 sin A cos A = sin 2A = 2.25 - 1 = 1.25 = 5/4.

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