Bradford T. answered 01/14/21
Retired Engineer / Upper level math instructor
First multiply the numerator and denominator by the complex conjugate of the denominator.
This uses the fact that (x-yi)(x+yi) = x2+y2
(5-8i)(3-2i)/((3+2i)(3-2i)) = (15-10i-24i-16)/(9+4) =(-1-34i)/13
= (-1/13) + (-34/13)i
Here, a = -1/13 and b = -34/13