Question

三角函数cos²75°+cos²15°+cos75°cos15°的值为

Answer 1

cos平方75°+cos平方15°+cos75°乘cos15°
=sin²15°+cos²15°+cos75°cos15°
=1+cos75°cos15°
=1+sin15°cos15°
=1+(2sin15°cos15°)/2
=1+sin30°/2
=1+1/4
=5/4
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