| 3 | x | × | 3 | x | + | 7 | = | ( | 5 | − | x | ) | ( | 5 | − | x | ) |
| 方程左边 = | 9 | x | x | + | 7 |
| 9 | x | x | + | 7 | = | ( | 5 | − | x | ) | ( | 5 | − | x | ) |
| 方程右边 = | 5 | ( | 5 | − | x | ) | − | x | ( | 5 | − | x | ) |
| = | 5 | × | 5 | − | 5 | x | − | x | ( | 5 | − | x | ) |
| = | 25 | − | 5 | x | − | x | ( | 5 | − | x | ) |
| = | 25 | − | 5 | x | − | x | × | 5 | + | x | x |
| = | 25 | − | 10 | x | + | x | x |
| 9 | x | x | + | 7 | = | 25 | − | 10 | x | + | x | x |
| x1= | - | 9 4 |
| x2=1 |