1/0=infinity

1/5 = 0.2
1/0.2=5
1/0.0000000000000000000000000000002 =5000000000000000000000000000000

etc..

It's dangerous to go alone! Take this:
  http://mathforum.org/dr.math/faq/faq.divideby0.html

Be sure to scroll down to get a long list of all the arithmetic operations that make no fucking sense with infinity. The extended reals are useless.

Oh, and by the way:

And 0/0 is truly undefined: IEEE754 gives 0/0 = NaN (not a number).
0/0 is not undefined, it's indeterminate. Fucking fail for thinking a bunch of engineering standards properly define mathematics.