题目

x=sint,y=tsint+cost,求d^2y/dx^2It=π/4,急等啊

提问时间：2020-12-22

答案

dx/dt=cost
dy/dt=sint+tcost-sint=tcost
y'=dy/dx=(dy/dt)/(dx/dt)=t
y"=d^2y/dx^2=d(y')/dx=d(y')/dt/(dx/dt)=1/cost
当t=π/4时,y"=1/cos(π/4)=√2