求证1+sina+cosa分之sin2a=sina - 知识问答

求证1+sina+cosa分之sin2a=sina+cosa-1 求指点呀!

2个回答

sin2a / (1+sina+cosa)
=2sinacosa / (2sina/2cosa/2 +2cos^2 a/2)
=4sina/2cosa/2 cosa / [2cosa/(sina/2+cosa/2)]
=2sina/2(cos^2 a/2-sin^2 a/2) / (sina/2+cosa/2)
=2sina/2(cosa/2-sina/2)
=2sina/2cosa/2 -2sin^2 a/2
=sina+cosa-1

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