Any quadratic equation, ax^2 + bx + c = 0 can be rearranged into a(x - h)^2 = k, a > 0
A is positive and the square of a real number is nonnegative. Thus, if x is real, the left side is nonnegative. But sometimes, k is negative, so that a real solution for x wouldn’t work, and a complex solution becomes necessary.
