1. Completing saquares permits to extract square root fo find the solutions.
This is the general equation when you complete the squares:
A(x-h)^2 + k = 0
Then you can obtain [x - h]^2 = - K/A and now you can extract square root in both sides.
2) If k and A have the same sigh, then - K/A is negative and the square root has not real solutions, i.e. the solution will be complex.
