40 100 | x | + | ( | 87 | − | x | ) | × | 50 100 | = | 39 |
| 方程左边 = | 40 100 | x | + | 87 | × | 50 100 | − | x | × | 50 100 |
| = | 40 100 | x | + | 87 2 | − | x | × | 50 100 |
| = | - | 1 10 | x | + | 87 2 |
| - | 1 10 | x | + | 87 2 | = | 39 |
| - | 1 10 | x | = | 39 | − | 87 2 |
| - | 1 10 | x | = | - | 9 2 |
9 2 | = | 1 10 | x |
1 10 | x | = | 9 2 |
| x | = | 9 2 | ÷ | 1 10 |
| = | 9 2 | × | 10 |
| = | 9 | × | 5 |
| x | = | 45 |