| ( | 3 | x | − | 3 | ) | ( | 2 | x | + | 13 | ) | = | 3 | × | 2 |
| 方程左边 = | 3 | x | ( | 2 | x | + | 13 | ) | − | 3 | ( | 2 | x | + | 13 | ) |
| = | 3 | x | × | 2 | x | + | 3 | x | × | 13 | − | 3 | ( | 2 | x | + | 13 | ) |
| = | 6 | x | x | + | 39 | x | − | 3 | ( | 2 | x | + | 13 | ) |
| = | 6 | x | x | + | 39 | x | − | 3 | × | 2 | x | − | 3 | × | 13 |
| = | 6 | x | x | + | 39 | x | − | 6 | x | − | 39 |
| = | 6 | x | x | + | 33 | x | − | 39 |
| 6 | x | x | + | 33 | x | − | 39 | = | 3 | × | 2 |
| 方程右边 = | 6 |
| 6 | x | x | + | 33 | x | − | 39 | = | 6 |