切线方向 (a(1-cost),a sin(t))dx(t)/dt=a(1-cost),dy(t)/dt=a sintt=Pi/2对应的坐标为(a(Pi/2-1),a)切线方向（a(1-cos(Pi/2)),a sin(Pi/2))=a(1,1)法线(x-a(Pi/2-1))*1+(y-a)*1=0切线(x-a(Pi/2-1))/1=(y-a)/1...