Mathematica Evaluate limit relation between variables in Mathematica

[mvww]

Hello.
How do I evaluate, in Mathematica, limits like this:
"X+Y" when X is much bigger than Y, i.e., when Y/X->0. The unswer should be X+Y->X.

Regards.

 

[Bill Simpson]

I've never seen Mathematica take limits with respect to an expression. All the examples I've seen take limits with respect to a variable.

Perhaps you could see how to use this:

In[1]:= x+y/.y->10.^-100x

Out[1]= 1. x

 

[Hepth]

I always just use a scale variable and expand.

let z = x/y:

F[x_, y_] := x + y
Normal[Series[F[x, z x], {z, 0, 0}]]