Write x^2-12x+8 in vertex form.

The vertex form: y = a (x - h) ² + k

y = ax² + bx + c then h = - b/2a and k = f (h).

y = x² - 12x + 8

a = 1; b = - 12; c = 8

h = - (-12) / (2·1) = 12/2 = 6

k = f (6) = 6² - 12·6 + 8 = 36 - 72 + 8 = - 28

Answer: y = (x - 6) ² - 28.