| - | 9 | ÷ | a | × | ( | - | a | − | 3 | ) | = | 3 | ( | 3 | + | 9 | ÷ | a | ) |
| 方程两边同时乘以: | a |
| - | 9 | ( | - | a | − | 3 | ) | = | 3 | ( | 3 | + | 9 | ÷ | a | ) | a |
| 9 | a | + | 9 | × | 3 | = | 3 | ( | 3 | + | 9 | ÷ | a | ) | a |
| 9 | a | + | 9 | × | 3 | = | 3 | × | 3 | a | + | 3 | × | 9 | ÷ | a | × | a |
| 9 | a | + | 27 | = | 9 | a | + | 27 | ÷ | a | × | a |
| 9 | a | − | 9 | a | = | 27 | ÷ | 1 | × | 1 | − | 27 |
| 9 | a | − | 9 | a | = | 27 | − | 27 |
| 0 | a | = | 27 | − | 27 |
| 0 | a | = | 0 |