| ( | 40 | − | x | ) | ( | 20 | + | 2 | ) | = | 1200 |
| 方程左边 = | 40 | ( | 20 | + | 2 | ) | − | x | ( | 20 | + | 2 | ) |
| = | 40 | × | 20 | + | 40 | × | 2 | − | x | ( | 20 | + | 2 | ) |
| = | 800 | + | 80 | − | x | ( | 20 | + | 2 | ) |
| = | 880 | − | x | ( | 20 | + | 2 | ) |
| = | 880 | − | x | × | 20 | − | x | × | 2 |
| = | 880 | − | 22 | x |
| 880 | − | 22 | x | = | 1200 |
| - | 22 | x | = | 1200 | − | 880 |
| - | 22 | x | = | 320 |
| - | 320 | = | 22 | x |
| 22 | x | = | - | 320 |
| x | = | - | 320 | ÷ | 22 |
| = | - | 320 | × | 1 22 |
| = | - | 160 | × | 1 11 |
| x | = | - | 160 11 |
| x | = | - 14.545455 |