Prove that

C(n,r) + C(n,r-1) = C(n+1,r)


I got up to doing the common denominator on the left side but then I just don't know what to do from there..
I also tried starting with the right hand side and getting to the left hand side but couldn't work it out either

help @______@

that is just pascal's triangle identity, see the proof in http://2000clicks.com/mathhelp/CountingComboIdentities.aspx

thank you this helped a lot, finally got it