T=2π/w=2π,w=1
f(x)=sin(x+φ)=f(-x)=sin(-x+φ)
因为x为变量,所以x+φ=π-(-x+φ)+2kπ
2φ=π+2kπ,φ=π/2+kπ,0≦φ≦π
φ=π/2.
f(x)=sin(x+π/2)