| ( | x | − | 40 | ) | ( | 100 | − | 2 | ( | x | − | 60 | ) | ) | = | 2250 |
| 方程左边 = | x | ( | 100 | − | 2 | ( | x | − | 60 | ) | ) | − | 40 | ( | 100 | − | 2 | ( | x | − | 60 | ) | ) |
| = | x | × | 100 | − | x | × | 2 | ( | x | − | 60 | ) | − | 40 | ( | 100 | − | 2 | ( | x | − | 60 | ) | ) |
| = | 100 | x | − | x | × | 2 | x | + | x | × | 2 | × | 60 | − | 40 | ( | 100 | − | 2 | ( | x | − | 60 | ) | ) |
| = | 100 | x | − | x | × | 2 | x | + | x | × | 120 | − | 40 | ( | 100 | − | 2 | ( | x | − | 60 | ) | ) |
| = | 220 | x | − | x | × | 2 | x | − | 40 | ( | 100 | − | 2 | ( | x | − | 60 | ) | ) |
| = | 220 | x | − | x | × | 2 | x | − | 40 | × | 100 | + | 40 | × | 2 | ( | x | − | 60 | ) |
| = | 220 | x | − | x | × | 2 | x | − | 4000 | + | 80 | ( | x | − | 60 | ) |
| = | 220 | x | − | x | × | 2 | x | − | 4000 | + | 80 | x | − | 80 | × | 60 |
| = | 220 | x | − | x | × | 2 | x | − | 4000 | + | 80 | x | − | 4800 |
| = | 300 | x | − | x | × | 2 | x | − | 8800 |
| 300 | x | − | x | × | 2 | x | − | 8800 | = | 2250 |