| 4 | x | x | − | 3 | x | ( | 20 | − | x | ) | = | 5 | x | − | 7 | x | ( | 20 | − | x | ) | + | 10 |
| 方程左边 = | 4 | x | x | − | 3 | x | × | 20 | + | 3 | x | x |
| = | 4 | x | x | − | 60 | x | + | 3 | x | x |
| 4 | x | x | − | 60 | x | + | 3 | x | x | = | 5 | x | − | 7 | x | ( | 20 | − | x | ) | + | 10 |
| 方程右边 = | 5 | x | − | 7 | x | × | 20 | + | 7 | x | x | + | 10 |
| = | 5 | x | − | 140 | x | + | 7 | x | x | + | 10 |
| = | - | 135 | x | + | 7 | x | x | + | 10 |
| 4 | x | x | − | 60 | x | + | 3 | x | x | = | - | 135 | x | + | 7 | x | x | + | 10 |
| x= | 2 15 |