| 21 | ÷ | ( | x | − | 1 | ) | = | 21 | ÷ | x | + | 1 | ÷ | 2 |
| 方程两边同时乘以: | ( | x | − | 1 | ) | , | x |
| 21 | x | = | 21 | ( | x | − | 1 | ) | + | 1 | ÷ | 2 | × | ( | x | − | 1 | ) | x |
| 21 | x | = | 21 | x | − | 21 | × | 1 | + | 1 | ÷ | 2 | × | ( | x | − | 1 | ) | x |
| 21 | x | = | 21 | x | − | 21 | + | 1 2 | ( | x | − | 1 | ) | x |
| 21 | x | = | 21 | x | − | 21 | + | 1 2 | x | x | − | 1 2 | × | 1 | x |
| 21 | x | = | 21 | x | − | 21 | + | 1 2 | x | x | − | 1 2 | x |
| 21 | x | = | 41 2 | x | − | 21 | + | 1 2 | x | x |