الاجابة
نفرض أن x3 = u
u2 – 26u – 27 = 0
(u – 27)(u + 1) = 0
(u + 1) = 0 (u- 27) = 0
u = -1 u = 27
x3 = -1 x3 = 27
X = -1 x = 3