| ( | 25 | − | x | − | 15 | ) | ( | 15 | x | + | 200 | ) | = | 1560 |
| 方程左边 = | 25 | ( | 15 | x | + | 200 | ) | − | x | ( | 15 | x | + | 200 | ) | − | 15 | ( | 15 | x | + | 200 | ) |
| = | 25 | × | 15 | x | + | 25 | × | 200 | − | x | ( | 15 | x | + | 200 | ) | − | 15 | ( | 15 | x | + | 200 | ) |
| = | 375 | x | + | 5000 | − | x | ( | 15 | x | + | 200 | ) | − | 15 | ( | 15 | x | + | 200 | ) |
| = | 375 | x | + | 5000 | − | x | × | 15 | x | − | x | × | 200 | − | 15 | ( | 15 | x | + | 200 | ) |
| = | 175 | x | + | 5000 | − | x | × | 15 | x | − | 15 | ( | 15 | x | + | 200 | ) |
| = | 175 | x | + | 5000 | − | x | × | 15 | x | − | 15 | × | 15 | x | − | 15 | × | 200 |
| = | 175 | x | + | 5000 | − | x | × | 15 | x | − | 225 | x | − | 3000 |
| = | - | 50 | x | + | 2000 | − | x | × | 15 | x |
| - | 50 | x | + | 2000 | − | x | × | 15 | x | = | 1560 |
| x1= | - | 22 3 |
| x2=4 |