Pi

if pi goes on forever how can you know it doesn't repeat?

Pi is an irrational number: Pi is not equal to a/b for any pair (a,b) of natural numbers. You can find a proof of this here:

http://www.lrz-muenchen.de/~hr/numb/pi-irr.html

Moreover, at

http://en.wikipedia.org/wiki/Irrational_number#Decimal_expansions

it is explained why the decimal expansion of irrationals never repeat or terminate.