| ( | 600 | − | ( | x | − | 40 | ) | × | 10 | ) | ( | x | − | 30 | ) | = | 10000 |
| 方程左边 = | 600 | ( | x | − | 30 | ) | − | ( | x | − | 40 | ) | × | 10 | ( | x | − | 30 | ) |
| = | 600 | x | − | 600 | × | 30 | − | ( | x | − | 40 | ) | × | 10 | ( | x | − | 30 | ) |
| = | 600 | x | − | 18000 | − | ( | x | − | 40 | ) | × | 10 | ( | x | − | 30 | ) |
| = | 600 | x | − | 18000 | − | x | × | 10 | ( | x | − | 30 | ) | + | 40 | × | 10 | ( | x | − | 30 | ) |
| = | 600 | x | − | 18000 | − | x | × | 10 | ( | x | − | 30 | ) | + | 400 | ( | x | − | 30 | ) |
| = | 600 | x | − | 18000 | − | x | × | 10 | x | + | x | × | 10 | × | 30 | + | 400 | ( | x | − | 30 | ) |
| = | 600 | x | − | 18000 | − | x | × | 10 | x | + | x | × | 300 | + | 400 | ( | x | − | 30 | ) |
| = | 900 | x | − | 18000 | − | x | × | 10 | x | + | 400 | ( | x | − | 30 | ) |
| = | 900 | x | − | 18000 | − | x | × | 10 | x | + | 400 | x | − | 400 | × | 30 |
| = | 900 | x | − | 18000 | − | x | × | 10 | x | + | 400 | x | − | 12000 |
| = | 1300 | x | − | 30000 | − | x | × | 10 | x |
| 1300 | x | − | 30000 | − | x | × | 10 | x | = | 10000 |