Find all solutions of the equation $\displaystyle x^2+3x+8=0$ and express them in the form a+bi: (I have no idea what 'i' stands for)

I have to find 2 sets of numbers in which the first set b < 0, then another set with b > 0. A and B are both real numbers.

I can't find an easy way to factor it, and when I put it into the quadratic formula it isn't possible because you cant squareroot -26.