rational zero theorem is all combinations of p(factors of the constant) divided by q(factors of the first coefficient) 
factors of 8 are 1, 2, 4, 8
factors of 2 are 1, 2
so all possible rational zeros are all combinations of p/q
+/-   1/1, 1/2, 2/1, 2/2, 4/1, 4/2, 8/1, 8/2
Now there are some repeats in there so you have to leave those out and once we do that we get 
+/- 1, 1/2, 2, 4, 8 
Remember all those are plus OR minus