So the equation x 2 + b x + c = 0 becomes (x + b 2) 2 (b 2) 2 + c = 0. This can be rearranged to give (x + b 2) 2 = (b 2) 2 c which can then be solved by taking the square root of both sides.

Example x 2 6 x + 9 = 0 The equation factorises to give (x 3) (x 3) = 0 so there is just one solution to the equation, x = 3. The graph of y = x 2 6 x + 9 touches the x -axis at x = 3.