Question

2sin^2(π/4+x)怎样化成1-cos(2/π+2x)

Answer 1

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