| - | a | − | ( | 3 | − | 9 | a | ) | = | ( | 3 | − | 9 | a | ) | − | ( | - | 1 | − | 5 | a | ) |
| 方程左边 = | - | a | − | 3 | + | 9 | a |
| = | 8 | a | − | 3 |
| 8 | a | − | 3 | = | ( | 3 | − | 9 | a | ) | − | ( | - | 1 | − | 5 | a | ) |
| 方程右边 = | 3 | − | 9 | a | − | ( | - | 1 | − | 5 | a | ) |
| = | 3 | − | 9 | a | + | 1 | + | 5 | a |
| = | 4 | − | 4 | a |
| 8 | a | − | 3 | = | 4 | − | 4 | a |
| 8 | a | + | 4 | a | = | 4 | + | 3 |
| 12 | a | = | 4 | + | 3 |
| 12 | a | = | 7 |
| a | = | 7 | ÷ | 12 |
| = | 7 | × | 1 12 |
| a | = | 7 12 |
| a | = | 0.583333 |