E = (x-3)² + (x-3)(x+3)
E = (x-3)² + x² - 9
E = x² - 6x + 9 + x² - 9 = 2x² - 6x
a = 2
b = -6
c = 0
delta = b² - 4ac = 36
racine(delta) = 6
x1 = (-b+racine(delta))/2a = 3
x2 = (-b-racine(delta))/2a = 0
Et E = a(x-x1)(x-x2) = 2(x-3)(x-0)
E = 2x(x-3)
Si x = 5, E = 20