y'=cosx
y(2π/3)=sin(2π/3)=√3/2
y'(2π/3)=cos(2π/3)=-1/2
切线：y=-1/2*(x-2π/3)+√3/2
法线：y=2(x-2π/3)+√3/2*这个是什么意思？？求解就是乘号呀