| 4 | ( | x | + | 1 | ) | ( | x | + | 1 | ) | = | 25 |
| 方程左边 = | 4 | x | ( | x | + | 1 | ) | + | 4 | × | 1 | ( | x | + | 1 | ) |
| = | 4 | x | ( | x | + | 1 | ) | + | 4 | ( | x | + | 1 | ) |
| = | 4 | x | x | + | 4 | x | × | 1 | + | 4 | ( | x | + | 1 | ) |
| = | 4 | x | x | + | 4 | x | + | 4 | ( | x | + | 1 | ) |
| = | 4 | x | x | + | 4 | x | + | 4 | x | + | 4 | × | 1 |
| = | 4 | x | x | + | 4 | x | + | 4 | x | + | 4 |
| = | 4 | x | x | + | 8 | x | + | 4 |
| 4 | x | x | + | 8 | x | + | 4 | = | 25 |
| x1= | - | 7 2 |
| x2= | 3 2 |