The quadratic formula is unnecessary since

Note: Without seeing your working it's impossible to know what mistake(s) you've made in applying the quadratic formula. At a guess, I'd say you found the discriminant to be either 4 - 4(48) = -188 or -4 - 4(48) = -196 ...... both are wrong. It's (-2)^2 - 4(-48) = 4 - 4(-48) = 196.