| ( | x | − | 2 | ) | ( | 100 | + | 200 | x | ) | = | 300 |
| 方程左边 = | x | ( | 100 | + | 200 | x | ) | − | 2 | ( | 100 | + | 200 | x | ) |
| = | x | × | 100 | + | x | × | 200 | x | − | 2 | ( | 100 | + | 200 | x | ) |
| = | 100 | x | + | x | × | 200 | x | − | 2 | × | 100 | − | 2 | × | 200 | x |
| = | 100 | x | + | x | × | 200 | x | − | 200 | − | 400 | x |
| = | - | 300 | x | + | x | × | 200 | x | − | 200 |
| - | 300 | x | + | x | × | 200 | x | − | 200 | = | 300 |
| x2= | 5 2 |