16) Limits in 3-D

> g:=(x^2-y^2)/(x+y);

> limit(g,{x=0,y=0});

> f:=(x,y)->(x^2-y^2)/(x^2+y^2);

> limit(f(x,y),{x=0,y=0});

> plot3d(f(x,y),x=-3..3,y=-3..3,axes=boxed);