sin²(π+α)-sin(α+3π/2)cos(-α)+1的值为

sin²(π+α)-sin(α+3π/2)cos(-α)+1
=(-sina)²-(-cosa)*cosa+1
=sin²a+cos²a+1
=1+1
=2sin²(π+α)=(-sina)²有点搞不明白，麻烦详细说下，谢谢因为sin(π+α)=-sinα所以sin²(π+α)=[sin(π+α)]²=(-sinα)²