| 20 | × | 32 | − | ( | 10 | × | 10 | × | 3 | − | ( | 10 | − | x | ) | ( | 10 | − | x | ) | × | 3 | ) | − | 12 | x | = | 540 |
| 方程左边 = | 640 | − | ( | 10 | × | 10 | × | 3 | − | ( | 10 | − | x | ) | ( | 10 | − | x | ) | × | 3 | ) | − | 12 | x |
| 640 | − | ( | 10 | × | 10 | × | 3 | − | ( | 10 | − | x | ) | ( | 10 | − | x | ) | × | 3 | ) | − | 12 | x | = | 540 |
| 方程左边 = | 640 | − | 10 | × | 10 | × | 3 | + | ( | 10 | − | x | ) | ( | 10 | − | x | ) | × | 3 | − | 12 | x |
| = | 640 | − | 300 | + | ( | 10 | − | x | ) | ( | 10 | − | x | ) | × | 3 | − | 12 | x |
| = | 340 | + | ( | 10 | − | x | ) | ( | 10 | − | x | ) | × | 3 | − | 12 | x |
| = | 340 | + | 10 | ( | 10 | − | x | ) | × | 3 | − | x | ( | 10 | − | x | ) | × | 3 | − | 12 | x |
| = | 340 | + | 30 | ( | 10 | − | x | ) | − | x | ( | 10 | − | x | ) | × | 3 | − | 12 | x |
| = | 340 | + | 30 | × | 10 | − | 30 | x | − | x | ( | 10 | − | x | ) | × | 3 | − | 12 | x |
| = | 340 | + | 300 | − | 30 | x | − | x | ( | 10 | − | x | ) | × | 3 | − | 12 | x |
| = | 640 | − | 42 | x | − | x | ( | 10 | − | x | ) | × | 3 |
| = | 640 | − | 42 | x | − | x | × | 10 | × | 3 | + | x | x | × | 3 |
| = | 640 | − | 42 | x | − | x | × | 30 | + | x | x | × | 3 |
| = | 640 | − | 72 | x | + | x | x | × | 3 |
| 640 | − | 72 | x | + | x | x | × | 3 | = | 540 |