Question

高等数学含参数求导问题

高等数学含参数求导问题麻烦帮忙看下这道题，划线部分是怎么求出来的，求详细过程

Answer 1

x=sint =>dx/dt = cost
y=tsint +cost => dy/dt = tcost + sint - sint = tcost
dy/dx = (dy/dt )/(dx/dt ) = tcost/cost = t
d^2y/dx^2
=d/dt ( dy/dx ) / (dx/dt)
=1/cost
d^2y/dx^2 | t=π/4
=1/cos(π/4)
=√2