| ( | 4 | − | 2 | x | ) | ( | 5 | − | 2 | x | ) | = | 4 | ÷ | 63 |
| 方程左边 = | 4 | ( | 5 | − | 2 | x | ) | − | 2 | x | ( | 5 | − | 2 | x | ) |
| = | 4 | × | 5 | − | 4 | × | 2 | x | − | 2 | x | ( | 5 | − | 2 | x | ) |
| = | 20 | − | 8 | x | − | 2 | x | ( | 5 | − | 2 | x | ) |
| = | 20 | − | 8 | x | − | 2 | x | × | 5 | + | 2 | x | × | 2 | x |
| = | 20 | − | 8 | x | − | 10 | x | + | 4 | x | x |
| = | 20 | − | 18 | x | + | 4 | x | x |
| 20 | − | 18 | x | + | 4 | x | x | = | 4 | ÷ | 63 |
| 方程右边 = | 4 63 |
| 20 | − | 18 | x | + | 4 | x | x | = | 4 63 |