| ( | x | − | 30 | ) | ( | - | 10 | + | 1000 | ) | = | 12000 |
| 方程左边 = | x | ( | - | 10 | + | 1000 | ) | − | 30 | ( | - | 10 | + | 1000 | ) |
| = | - | x | × | 10 | + | x | × | 1000 | − | 30 | ( | - | 10 | + | 1000 | ) |
| = | 990 | x | − | 30 | ( | - | 10 | + | 1000 | ) |
| = | 990 | x | + | 30 | × | 10 | − | 30 | × | 1000 |
| = | 990 | x | + | 300 | − | 30000 |
| = | 990 | x | − | 29700 |
| 990 | x | − | 29700 | = | 12000 |
| 990 | x | = | 12000 | + | 29700 |
| 990 | x | = | 41700 |
| x | = | 41700 | ÷ | 990 |
| = | 41700 | × | 1 990 |
| = | 1390 | × | 1 33 |
| x | = | 1390 33 |
| x | = | 42.121212 |