Ok, I know how to start this problem, but the synthetic division is confusing me a little.

Use synthetic division to verify the upper and/or lower bounds of the zeros of f.

f(x) = 2x^4 - 8x + 3

Upper bound: x = 3; Lower bound: x = -4

So the possible real zeros I think are:

plus or minus 1/2, plus or minus 1.5

Now, I am confused. Can anyone help?