| 9 | ( | a | − | 1 | ) | − | 12 | − | 1 | + | 2 | a | = | 0 |
| Left side of the equation = | 9 | ( | a | − | 1 | ) | − | 13 | + | 2 | a |
| 9 | ( | a | − | 1 | ) | − | 13 | + | 2 | a | = | 0 |
| Left side of the equation = | 9 | a | − | 9 | × | 1 | − | 13 | + | 2 | a |
| = | 9 | a | − | 9 | − | 13 | + | 2 | a |
| = | 11 | a | − | 22 |
| 11 | a | − | 22 | = | 0 |
| 11 | a | = | 0 | + | 22 |
| 11 | a | = | 22 |
| a | = | 22 | ÷ | 11 |
| = | 22 | × | 1 11 |
| = | 2 | × | 1 |
| a | = | 2 |