2sin^2(π/4+x)怎样化成1-cos(2/π+2x)=[cos(Pi/4+x)]^2-[sin(Pi/4+x)]^2这一步怎么来的?

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2sin^2(π/4+x)怎样化成1-cos(2/π+2x)=[cos(Pi/4+x)]^2-[sin(Pi/4+x)]^2这一步怎么来的?
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2sin^2(π/4+x)怎样化成1-cos(2/π+2x)=[cos(Pi/4+x)]^2-[sin(Pi/4+x)]^2这一步怎么来的?
2sin^2(π/4+x)怎样化成1-cos(2/π+2x)
=[cos(Pi/4+x)]^2-[sin(Pi/4+x)]^2
这一步怎么来的?

2sin^2(π/4+x)怎样化成1-cos(2/π+2x)=[cos(Pi/4+x)]^2-[sin(Pi/4+x)]^2这一步怎么来的?
cos(2/π+2x)
=cos[2(Pi/4+x)]
=[cos(Pi/4+x)]^2-[sin(Pi/4+x)]^2
=1-[sin(Pi/4+x)]^2-[sin(Pi/4+x)]^2
所以:2sin^2(π/4+x)=1-cos(π/2+2x)
这一步是公式:cos2x=(cosx)^2-(sinx)^2