求值【sin(2π-α)sin(π+α)cos(-

求值【sin(2π-α)sin(π+α)cos(-π-α)】/【sin(3π-α)-cos(π-α)】

2个回答

sin(2π-α)=-sinα,sin(π+α)=-sinα,cos(-π-α)=-cosα,sin(3π-α)=sinα,cos(π-α)=-cosα
上式=-sinα*sinα*cosα/(sinα+cosα)
就是这样了吧

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