已知函数f(x)=sinx/2cosx/2+cos平方x/2-1/2

1、
f(x)=1/2*sinx+(1+cosx)/2-1/2
=1/2(sinx+cosx)
=(√2/2)(sinx*√2/2+cosx*√2/2)
=(√2/2)(sinxcosπ/4+cosxsinπ/4)
=(√2/2)sin(x+π/4)
f(a)=(√2/2)sin(a+π/4)=√2/4
sin(a+π/4)=1/2
π/4