| 200 | ( | ( | 10 | − | x | ) | − | 8 | ) | = | 640 |
| 方程左边 = | 200 | ( | 10 | − | x | ) | − | 200 | × | 8 |
| = | 200 | ( | 10 | − | x | ) | − | 1600 |
| = | 200 | × | 10 | − | 200 | x | − | 1600 |
| = | 2000 | − | 200 | x | − | 1600 |
| = | 400 | − | 200 | x |
| 400 | − | 200 | x | = | 640 |
| - | 200 | x | = | 640 | − | 400 |
| - | 200 | x | = | 240 |
| - | 240 | = | 200 | x |
| 200 | x | = | - | 240 |
| x | = | - | 240 | ÷ | 200 |
| = | - | 240 | × | 1 200 |
| = | - | 6 | × | 1 5 |
| x | = | - | 6 5 |
| x | = | - 1.2 |