Selesaikan persamaan kuadrat berikut dengan rumus abc x2-3x-28=0

x² - 3x -28 = 0
(x-7)(x+4) = 0
x¹ = 7
x² = -4

x¹'² = (3±√9-(-112))/2 = (3±11)/2
x¹ = (3+11)/2 = 7
x² = (3-11)/2 = -4