d²F(x,y)/dxdy
F(x,y)对x,y求导就可以了
若y上限是a
Fx(x)=lim(y->a)dF(x,y)/dy
这里由於y无上限
Fx(x)=lim(y->无穷大)dF(x,y)/dy
=limy->无穷 1-e^(-x)+e^(-y) - e^(-x-y)
=1-e^(-x)+0-0
=1-e^(-x)
F(1,2)=1-1/e-1/e²+1/e³
d²F(x,y)/dxdy
F(x,y)对x,y求导就可以了
若y上限是a
Fx(x)=lim(y->a)dF(x,y)/dy
这里由於y无上限
Fx(x)=lim(y->无穷大)dF(x,y)/dy
=limy->无穷 1-e^(-x)+e^(-y) - e^(-x-y)
=1-e^(-x)+0-0
=1-e^(-x)
F(1,2)=1-1/e-1/e²+1/e³