| ( | 240 | − | 4 5 | x | ) | ( | x | − | 2500 | ) | = | 0 |
| 方程左边 = | 240 | ( | x | − | 2500 | ) | − | 4 5 | x | ( | x | − | 2500 | ) |
| = | 240 | x | − | 240 | × | 2500 | − | 4 5 | x | ( | x | − | 2500 | ) |
| = | 240 | x | − | 600000 | − | 4 5 | x | ( | x | − | 2500 | ) |
| = | 240 | x | − | 600000 | − | 4 5 | x | x | + | 4 5 | x | × | 2500 |
| = | 240 | x | − | 600000 | − | 4 5 | x | x | + | 2000 | x |
| = | 2240 | x | − | 600000 | − | 4 5 | x | x |
| 2240 | x | − | 600000 | − | 4 5 | x | x | = | 0 |