| ( | 500 | − | 40 | x | ) | ( | 4 | x | + | 10 | ) | = | 8000 |
| 方程左边 = | 500 | ( | 4 | x | + | 10 | ) | − | 40 | x | ( | 4 | x | + | 10 | ) |
| = | 500 | × | 4 | x | + | 500 | × | 10 | − | 40 | x | ( | 4 | x | + | 10 | ) |
| = | 2000 | x | + | 5000 | − | 40 | x | ( | 4 | x | + | 10 | ) |
| = | 2000 | x | + | 5000 | − | 40 | x | × | 4 | x | − | 40 | x | × | 10 |
| = | 2000 | x | + | 5000 | − | 160 | x | x | − | 400 | x |
| = | 1600 | x | + | 5000 | − | 160 | x | x |
| 1600 | x | + | 5000 | − | 160 | x | x | = | 8000 |
| x1= | 5 2 |
| x2= | 15 2 |