| ( | 20 | − | x | ) | ( | 20 | − | x | ) | ÷ | 40 | − | x | ( | 20 | − | x | ) | ÷ | 20 | = | 0 |
| 方程左边 = | 20 | ( | 20 | − | x | ) | × | 1 40 | − | x | ( | 20 | − | x | ) | × | 1 40 | − | x | ( | 20 | − | x | ) | × | 1 20 |
| = | 1 2 | ( | 20 | − | x | ) | − | x | ( | 20 | − | x | ) | × | 1 40 | − | x | ( | 20 | − | x | ) | × | 1 20 |
| = | 1 2 | × | 20 | − | 1 2 | x | − | x | ( | 20 | − | x | ) | × | 1 40 | − | x | ( | 20 | − | x | ) | × | 1 20 |
| = | 10 | − | 1 2 | x | − | x | ( | 20 | − | x | ) | × | 1 40 | − | x | ( | 20 | − | x | ) | × | 1 20 |
| = | 10 | − | 1 2 | x | − | x | × | 20 | × | 1 40 | + | x | x | × | 1 40 | − | x | ( | 20 | − | x | ) | × | 1 20 |
| = | 10 | − | 1 2 | x | − | x | × | 1 2 | + | x | x | × | 1 40 | − | x | ( | 20 | − | x | ) | × | 1 20 |
| = | 10 | − | 1 | x | + | x | x | × | 1 40 | − | x | ( | 20 | − | x | ) | × | 1 20 |
| = | 10 | − | 1 | x | + | x | x | × | 1 40 | − | x | × | 20 | × | 1 20 | + | x | x | × | 1 20 |
| = | 10 | − | 1 | x | + | x | x | × | 1 40 | − | x | × | 1 | + | x | x | × | 1 20 |
| = | 10 | − | 2 | x | + | x | x | × | 1 40 | + | x | x | × | 1 20 |
| 10 | − | 2 | x | + | x | x | × | 1 40 | + | x | x | × | 1 20 | = | 0 |
| x1= | 20 3 |
| x2=20 |