f(x)=cos(x+π/4)sin(π/4-x)-1/2
= (cosxcosπ/4-sinxsinπ/4)(sinπ/4cosx-cosπ/4sinx)
= √2/2(cosx-sinx)*√2/2(cosx-sinx)-1/2
= 1/2(cosx-sinx)^2-1/2
= 1/2(cos^2x-2cosxsinx+sin^2x)-1/2
= 1/2(1-2cosxsinx)-1/2
= -sinxcosx
= -1/2sin2x
最小正周期 = 2π/2 = π
f(-x) = -1/2sin(-2x) = 1/2sin(2x) = -f(x),奇函数