标准答案
dx/dt=1-costdy/dt=sint所以对P(x,y)处切线的切线斜率=dy/dx=sint/(1-cost)=2cos(t/2)sin(t/2)/2sin^2(t/2)=cot(t/2)因为该切线与x轴倾角为a，所以tana=cot(t/2)a=π/2-t/2cosa/√y=cos(π/2-t/2)/√(1-cost)=sin(t/2)/√[2sin^2(t/2)]=√2/2
