| ( | 12 | + | 1 5 | x | ) | ( | 2000 | − | 10 | x | ) | − | 7 | × | 2000 | = | 20000 |
| 方程左边 = | ( | 12 | + | 1 5 | x | ) | ( | 2000 | − | 10 | x | ) | − | 14000 |
| ( | 12 | + | 1 5 | x | ) | ( | 2000 | − | 10 | x | ) | − | 14000 | = | 20000 |
| 方程左边 = | 12 | ( | 2000 | − | 10 | x | ) | + | 1 5 | x | ( | 2000 | − | 10 | x | ) | − | 14000 |
| = | 12 | × | 2000 | − | 12 | × | 10 | x | + | 1 5 | x | ( | 2000 | − | 10 | x | ) | − | 14000 |
| = | 24000 | − | 120 | x | + | 1 5 | x | ( | 2000 | − | 10 | x | ) | − | 14000 |
| = | 10000 | − | 120 | x | + | 1 5 | x | ( | 2000 | − | 10 | x | ) |
| = | 10000 | − | 120 | x | + | 1 5 | x | × | 2000 | − | 1 5 | x | × | 10 | x |
| = | 10000 | − | 120 | x | + | 400 | x | − | 2 | x | x |
| = | 10000 | + | 280 | x | − | 2 | x | x |
| 10000 | + | 280 | x | − | 2 | x | x | = | 20000 |