| ( | x | − | 50 | ) | ( | 300 | − | 10 | ( | x | − | 60 | ) | ) | = | 3000 |
| 方程左边 = | x | ( | 300 | − | 10 | ( | x | − | 60 | ) | ) | − | 50 | ( | 300 | − | 10 | ( | x | − | 60 | ) | ) |
| = | x | × | 300 | − | x | × | 10 | ( | x | − | 60 | ) | − | 50 | ( | 300 | − | 10 | ( | x | − | 60 | ) | ) |
| = | 300 | x | − | x | × | 10 | x | + | x | × | 10 | × | 60 | − | 50 | ( | 300 | − | 10 | ( | x | − | 60 | ) | ) |
| = | 300 | x | − | x | × | 10 | x | + | x | × | 600 | − | 50 | ( | 300 | − | 10 | ( | x | − | 60 | ) | ) |
| = | 900 | x | − | x | × | 10 | x | − | 50 | ( | 300 | − | 10 | ( | x | − | 60 | ) | ) |
| = | 900 | x | − | x | × | 10 | x | − | 50 | × | 300 | + | 50 | × | 10 | ( | x | − | 60 | ) |
| = | 900 | x | − | x | × | 10 | x | − | 15000 | + | 500 | ( | x | − | 60 | ) |
| = | 900 | x | − | x | × | 10 | x | − | 15000 | + | 500 | x | − | 500 | × | 60 |
| = | 900 | x | − | x | × | 10 | x | − | 15000 | + | 500 | x | − | 30000 |
| = | 1400 | x | − | x | × | 10 | x | − | 45000 |
| 1400 | x | − | x | × | 10 | x | − | 45000 | = | 3000 |