y=sinx,y'=cosx,
x=π/3时y=√3/2,y'=1/2,切线方程是y-√3/2=（1/2）(x-π/3),法线方程是y-√3/2=-2(x-π/3).
x=π/2时y=1,y'=0,切线方程是y-1=0,法线方程是x-π/2=0.