| ( | 12 | − | 3 | x | ) | ( | 9 | − | 2 | x | ) | = | 45 |
| 方程左边 = | 12 | ( | 9 | − | 2 | x | ) | − | 3 | x | ( | 9 | − | 2 | x | ) |
| = | 12 | × | 9 | − | 12 | × | 2 | x | − | 3 | x | ( | 9 | − | 2 | x | ) |
| = | 108 | − | 24 | x | − | 3 | x | ( | 9 | − | 2 | x | ) |
| = | 108 | − | 24 | x | − | 3 | x | × | 9 | + | 3 | x | × | 2 | x |
| = | 108 | − | 24 | x | − | 27 | x | + | 6 | x | x |
| = | 108 | − | 51 | x | + | 6 | x | x |
| 108 | − | 51 | x | + | 6 | x | x | = | 45 |
| x1= | 3 2 |
| x2=7 |