已知函数f(x)=cos^4 x -2sinx *cosx-sin^4 x

1.原式=（cos^x+sin^x)(cos^x-sin^x)-2sinxcosx
=(cos^x-sin^x)-sin2x
=cos2x-sin2x=根号2sin(π/4-2x)
T=2π/(π/4)=8
2.由题,2kπ-π/2