【1】由“倍角公式”可得：cos2x=1-2sin²x.sin2x=2sinxcosx.∴2sin²x=1-cos2x.2sinxcosx=sin2x.∴函数f(x)=2sin²x+2sinxcosx-1=1-cos2x+sin2x-1=sin2x-cos2x=(√2)sin[2x-(π/4)].即题设中的函数可化...=sin2x-cos2x=(√2)sin[2x-(π/4)].就这里不懂