| ( | 7500 | ÷ | x | ) | + | ( | 10000 | ÷ | ( | x | + | 112 5 | ) | ) | = | 72 |
| 7500 | ÷ | x | + | ( | 10000 | ÷ | ( | x | + | 112 5 | ) | ) | = | 72 |
| 方程两边同时乘以: | x |
| 7500 | + | ( | 10000 | ÷ | ( | x | + | 112 5 | ) | ) | x | = | 72 | x |
| 7500 | + | 10000 | ÷ | ( | x | + | 112 5 | ) | × | x | = | 72 | x |
| 方程两边同时乘以: | ( | x | + | 112 5 | ) |
| 7500 | ( | x | + | 112 5 | ) | + | 10000 | x | = | 72 | x | ( | x | + | 112 5 | ) |
| 7500 | x | + | 7500 | × | 112 5 | + | 10000 | x | = | 72 | x | ( | x | + | 112 5 | ) |
| 7500 | x | + | 7500 | × | 112 5 | + | 10000 | x | = | 72 | x | x | + | 72 | x | × | 112 5 |
| 7500 | x | + | 168000 | + | 10000 | x | = | 72 | x | x | + | 8064 5 | x |
| 17500 | x | + | 168000 | = | 72 | x | x | + | 8064 5 | x |