Resposta :
x² - 8x + 7 = 0
a = 1
b = - 8
c = 7
delta = b² - 4*a*c
delta = (- 8)² - 4*1*7
delta = 64 - 28
delta = 36
x1 = (- b + raiz de delta) / 2*a = (+ 8 + 6) / 2*1 = 14 / 2 = 7
x2 = (- b - raiz de delta) / 2*a = (+ 8 - 6) / 2*1 = 2 / 2 = 1.
S = {1; 7}.