x=sint,y=cos2t,求dy/dx

题目

x=sint,y=cos2t,求dy/dx
不好意思..忘了x=1/2

答案

x=sint,所以dx/dt=cost
y=cos2t,所以dy/dt=-sin2t*(2t)'=-2sin2t=-4sintcost
dy/dx=(-4sintcost)/cost
=-4sint
=-4x