| ( | 1 | ÷ | s | ) | + | ( | 1 | ÷ | s | + | 5 | ) | + | ( | 1 | ÷ | s | + | 2 | ) | = | 0 |
| 1 | ÷ | s | + | ( | 1 | ÷ | s | + | 5 | ) | + | ( | 1 | ÷ | s | + | 2 | ) | = | 0 |
| 方程两边同时乘以: | s |
| 1 | + | ( | 1 | ÷ | s | + | 5 | ) | s | + | ( | 1 | ÷ | s | + | 2 | ) | s | = | 0 |
| 1 | + | 1 | ÷ | s | × | s | + | 5 | s | + | ( | 1 | ÷ | s | + | 2 | ) | s | = | 0 |
| 1 | + | 1 | ÷ | 1 | × | 1 | + | 5 | s | + | 1 | ÷ | s | × | s | + | 2 | s | = | 0 |
| 1 | + | 1 | + | 5 | s | + | 1 | ÷ | s | × | s | + | 2 | s | = | 0 |
| 2 | + | 7 | s | + | 1 | ÷ | s | × | s | = | 0 |
| 7 | s | = | 0 | − | 2 | − | 1 | ÷ | 1 | × | 1 |
| 7 | s | = | 0 | − | 2 | − | 1 |
| 7 | s | = | - | 3 |
| s | = | - | 3 | ÷ | 7 |
| = | - | 3 | × | 1 7 |
| s | = | - | 3 7 |
| s | = | - 0.428571 |