dqqcqc
幼苗
共回答了24个问题采纳率:83.3% 举报
解
2sin(x-π/4)sin(x+π/4)
=2sin(x-π/4)sin[π/2+(x-π/4)]
=2sin(x-π/4)cos(x-π/4)
=sin[2(x-π/4)]
=sin(2x-π/2)
=sin[-(π/2-2x)]
=-sin(π/2-2x)
=-cos2x
=-(cos²x-sin²x)
=sin²x-cos²x
=(sinx-cosx)(sinx+cosx)
1年前
追问
8
举报
dqqcqc
这是一个诱导公式 sin(π/2+a)=cosa sin(π/2-a)=cosa cos(π/2+a)=-sina cos(π/2-a)=sina 这些必须记住