| 750 | ÷ | ( | 750 | + | X | ) | = | 21 20 |
| 方程两边同时乘以: | ( | 750 | + | X | ) |
| 750 | = | 21 20 | ( | 750 | + | X | ) |
| 750 | = | 21 20 | × | 750 | + | 21 20 | X |
| 750 | = | 1575 2 | + | 21 20 | X |
| - | 21 20 | X | = | 1575 2 | − | 750 |
| - | 21 20 | X | = | 75 2 |
| - | 75 2 | = | 21 20 | X |
21 20 | X | = | - | 75 2 |
| X | = | - | 75 2 | ÷ | 21 20 |
| = | - | 75 2 | × | 20 21 |
| = | - | 25 | × | 10 7 |
| X | = | - | 250 7 |
| X | = | - 35.714286 |