If you prove the n=3 case for AM-GM, as has been suggested, it fall into place pretty quick. This is the method I've learnt for proving it, if anyone is interested:
First do the simple part and prove (x + y)/2 ≥ √(xy) ... (1)
Let R = (x+y+z)/3
R = (R + x + y + z)/4
&ge...