因为f(-x)=f(x),且f(-x+π)=f(x)
所以f(-x)=f(-x+π)
f(-7π/3)=f(-7π/3+π)=f(-7π/3+π+π)=f(-π/3)
因为f(-x)=f(x),所以f(-π/3)=f(π/3)
0＜π/3＜π/2,所以,f(π/3)=sin(π/3)=√3/2