| 3 | ( | - | 3 | x | − | 12 | ) | + | 8 | ( | 5 | x | + | 1 | ) | + | 12 | = | - | 16 |
| 方程左边 = | - | 3 | × | 3 | x | − | 3 | × | 12 | + | 8 | ( | 5 | x | + | 1 | ) | + | 12 |
| = | - | 9 | x | − | 36 | + | 8 | ( | 5 | x | + | 1 | ) | + | 12 |
| = | - | 9 | x | − | 24 | + | 8 | ( | 5 | x | + | 1 | ) |
| = | - | 9 | x | − | 24 | + | 8 | × | 5 | x | + | 8 | × | 1 |
| = | - | 9 | x | − | 24 | + | 40 | x | + | 8 |
| = | 31 | x | − | 16 |
| 31 | x | − | 16 | = | - | 16 |
| 31 | x | = | - | 16 | + | 16 |
| 31 | x | = | - | 0 |
| x | = | - | 0 | ÷ | 31 |
| = | - | 0 | × | 1 31 |
| x | = | 0 |