f(x)=sin(x/2)cos(x/2)+cos^2(x/2)-1.=(1/2)sinx+(1+cosx)/2-1.=(1/2)sinx+(1/2)cosx-1/2.=(1/2)(sinx+cosx)-1/2.∴f(x)=(√2/2)sin(x+π/4)-1/2.f(x)的最小正周期T=2π;∵sinx的递减区间是x∈[2kπ+π/2,2kπ+3π/2...