Tìm x biết (x – 3)^3 – (x – 3)(x^2 + 3x + 9) + 9(x + 1)^2 = 15.
Giải thích
(x – 3)3 – (x – 3)(x2 + 3x + 9) + 9(x + 1)2 = 15
x3 – 9x2 + 27x – 27 – (x3 + 3x2 + 9x – 3x2 – 9x – 27) + 9(x2 + 2x + 1) – 15 = 0
x3 – 9x2 + 27x – 27 – x3 + 27 + 9x2 + 18x + 9 – 15 = 0
45x – 6 = 0
x = 645.