当t=π/6时，x=sint=1/2，y=cos2t=1/2所以，切点为(1/2,1/2)切线的斜率k=dy/dx=(dy/dt)/(dx/dt)=(cos2t)'/(sint)/=-2sin2t/cost=-4sintcost/cost=-4sint所以，切点处切线的斜率为k'=-4sin(π/6)=-2所以，切线方程为：y-(1/2)=-2[x-(1/2)]即：y=-2x+(3/2)
