| 5000 | ( | 1 | + | X | ) | ( | 1 | + | X | ) | = | 7200 |
| 方程左边 = | 5000 | × | 1 | ( | 1 | + | X | ) | + | 5000 | X | ( | 1 | + | X | ) |
| = | 5000 | ( | 1 | + | X | ) | + | 5000 | X | ( | 1 | + | X | ) |
| = | 5000 | × | 1 | + | 5000 | X | + | 5000 | X | ( | 1 | + | X | ) |
| = | 5000 | + | 5000 | X | + | 5000 | X | ( | 1 | + | X | ) |
| = | 5000 | + | 5000 | X | + | 5000 | X | × | 1 | + | 5000 | X | X |
| = | 5000 | + | 5000 | X | + | 5000 | X | + | 5000 | X | X |
| = | 5000 | + | 10000 | X | + | 5000 | X | X |
| 5000 | + | 10000 | X | + | 5000 | X | X | = | 7200 |
| X1= | - | 11 5 |
| X2= | 1 5 |