函数f(x)是以π/2为最小正周期的函数f(x+π/2)=f(x)
f(17π/6)=f(5π/6+π/2*4)=f(5π/6）=f(π/3+π/2)=(fπ/3)
因为f(π/3)=1,所以f(17π/6)=1