| ( | 3 | − | x | ) | ( | 5000 | + | 5000 | x | ) | = | 0 |
| 方程左边 = | 3 | ( | 5000 | + | 5000 | x | ) | − | x | ( | 5000 | + | 5000 | x | ) |
| = | 3 | × | 5000 | + | 3 | × | 5000 | x | − | x | ( | 5000 | + | 5000 | x | ) |
| = | 15000 | + | 15000 | x | − | x | ( | 5000 | + | 5000 | x | ) |
| = | 15000 | + | 15000 | x | − | x | × | 5000 | − | x | × | 5000 | x |
| = | 15000 | + | 10000 | x | − | x | × | 5000 | x |
| 15000 | + | 10000 | x | − | x | × | 5000 | x | = | 0 |