| ( | 20 | − | 2 | x | ) | ( | 14 | − | 2 | x | ) | = | 160 |
| 方程左边 = | 20 | ( | 14 | − | 2 | x | ) | − | 2 | x | ( | 14 | − | 2 | x | ) |
| = | 20 | × | 14 | − | 20 | × | 2 | x | − | 2 | x | ( | 14 | − | 2 | x | ) |
| = | 280 | − | 40 | x | − | 2 | x | ( | 14 | − | 2 | x | ) |
| = | 280 | − | 40 | x | − | 2 | x | × | 14 | + | 2 | x | × | 2 | x |
| = | 280 | − | 40 | x | − | 28 | x | + | 4 | x | x |
| = | 280 | − | 68 | x | + | 4 | x | x |
| 280 | − | 68 | x | + | 4 | x | x | = | 160 |