| ( | x | − | 4 | ) | ( | 500 | − | 20 | x | − | 50 | ÷ | 20 | ) | = | 8000 |
| 方程左边 = | x | ( | 500 | − | 20 | x | − | 50 | ÷ | 20 | ) | − | 4 | ( | 500 | − | 20 | x | − | 50 | ÷ | 20 | ) |
| = | x | × | 500 | − | x | × | 20 | x | − | x | × | 50 | ÷ | 20 | − | 4 | ( | 500 | − | 20 | x | − | 50 | ÷ | 20 | ) |
| = | x | × | 500 | − | x | × | 20 | x | − | x | × | 5 2 | − | 4 | ( | 500 | − | 20 | x | − | 50 | ÷ | 20 | ) |
| = | 995 2 | x | − | x | × | 20 | x | − | 4 | ( | 500 | − | 20 | x | − | 50 | ÷ | 20 | ) |
| = | 995 2 | x | − | x | × | 20 | x | − | 4 | × | 500 | + | 4 | × | 20 | x | + | 4 | × | 50 |
| = | 995 2 | x | − | x | × | 20 | x | − | 2000 | + | 80 | x | + | 10 |
| = | 1155 2 | x | − | x | × | 20 | x | − | 1990 |
1155 2 | x | − | x | × | 20 | x | − | 1990 | = | 8000 |