| ( | 100 | + | x | ) | ( | 8 | − | ( | x | − | 100 | ) | ÷ | 10 | ) | = | 1200 |
| 方程左边 = | 100 | ( | 8 | − | ( | x | − | 100 | ) | ÷ | 10 | ) | + | x | ( | 8 | − | ( | x | − | 100 | ) | ÷ | 10 | ) |
| = | 100 | × | 8 | − | 100 | ( | x | − | 100 | ) | ÷ | 10 | + | x | ( | 8 | − | ( | x | − | 100 | ) | ÷ | 10 | ) |
| = | 800 | − | 10 | ( | x | − | 100 | ) | + | x | ( | 8 | − | ( | x | − | 100 | ) | ÷ | 10 | ) |
| = | 800 | − | 10 | x | + | 10 | × | 100 | + | x | ( | 8 | − | ( | x | − | 100 | ) | ÷ | 10 | ) |
| = | 800 | − | 10 | x | + | 1000 | + | x | ( | 8 | − | ( | x | − | 100 | ) | ÷ | 10 | ) |
| = | 1800 | − | 10 | x | + | x | ( | 8 | − | ( | x | − | 100 | ) | ÷ | 10 | ) |
| = | 1800 | − | 10 | x | + | x | × | 8 | − | x | ( | x | − | 100 | ) | ÷ | 10 |
| = | 1800 | − | 2 | x | − | x | ( | x | − | 100 | ) | × | 1 10 |
| = | 1800 | − | 2 | x | − | x | x | × | 1 10 | + | x | × | 100 | × | 1 10 |
| = | 1800 | − | 2 | x | − | x | x | × | 1 10 | + | x | × | 10 |
| = | 1800 | + | 8 | x | − | x | x | × | 1 10 |
| 1800 | + | 8 | x | − | x | x | × | 1 10 | = | 1200 |