设{x=ln√(1+t^2),y=arctant,求 dy/dx及d^2·y/d·x^2

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设{x=ln√(1+t^2),y=arctant,求 dy/dx及d^2·y/d·x^2

设{x=ln√(1+t^2),y=arctant,求 dy/dx及d^2·y/d·x^2
设{x=ln√(1+t^2),y=arctant,求 dy/dx及d^2·y/d·x^2

设{x=ln√(1+t^2),y=arctant,求 dy/dx及d^2·y/d·x^2
这是参数方程求导
x'=t/(1+t^2)
y'=1/(1+t^2)
x''= [(1+t^2)-t*2t]/(1+t^2)^2=(1-t^2)/(1+t^2)^2
y''=-2t/(1+t^2)^2
dy/dx=y'/x'=1/t
d^2y/dx^2=(x'y''-x''y')/(x')^3
=[-2t^2/(1+t^2)^3-(1-t^2)/(1+t^2)^3]/[t/(1+t^2)]^3
=(-t^2-1)/t^3