Đáp án:
x . (3x + 2) + (x + 1)² - (2x - 5)(2x + 5) = 0
3x² + 2x + (x² + 2x1 + 1²) - [(2x)² - 5²] = 0
3x² + 2x + x² + 2x + 1 - 4x² + 25 = 0
(3x² + x² - 4x²) + (2x + 2x) + (1 + 25) = 0
0 + 4x + 26 = 0
4x + 26 = 0
4x = 0 - 26
4x = -26
x = -26 : 4
Vậy x = -6,5