| ( | ( | 3000 | − | x | ) | × | 7 20 | + | 450 | ) | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) | = | x | − | 1 20 | × | 3000 |
| 方程左边 = | ( | 3000 | − | x | ) | × | 7 20 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 3000 | × | 7 20 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) | − | x | × | 7 20 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1050 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) | − | x | × | 7 20 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1050 | × | 1 | + | 1050 | × | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | − | x | × | 7 20 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1050 | + | 1 10 | ( | 3000 | − | x | ) | − | x | × | 7 20 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1050 | + | 1 10 | × | 3000 | − | 1 10 | x | − | x | × | 7 20 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1050 | + | 300 | − | 1 10 | x | − | x | × | 7 20 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1350 | − | 1 10 | x | − | x | × | 7 20 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1350 | − | 1 10 | x | − | x | × | 7 20 | × | 1 | − | x | × | 7 20 | × | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | + | 450 |
| = | 1350 | − | 1 10 | x | − | x | × | 7 20 | − | x | × | 1 30000 | ( | 3000 | − | x | ) | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1350 | − | 9 20 | x | − | x | × | 1 30000 | ( | 3000 | − | x | ) | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1350 | − | 9 20 | x | − | x | × | 1 30000 | × | 3000 | + | x | × | 1 30000 | x | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1350 | − | 9 20 | x | − | x | × | 1 10 | + | x | × | 1 30000 | x | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1350 | − | 11 20 | x | + | x | × | 1 30000 | x | + | 450 | ( | 1 | + | 2 | ( | 3000 | − | x | ) | ÷ | 21000 | ) |
| = | 1350 | − | 11 20 | x | + | x | × | 1 30000 | x | + | 450 | × | 1 | + | 450 | × | 2 | ( | 3000 | − | x | ) | ÷ | 21000 |
| = | 1350 | − | 11 20 | x | + | x | × | 1 30000 | x | + | 450 | + | 3 70 | ( | 3000 | − | x | ) |
| = | 1800 | − | 11 20 | x | + | x | × | 1 30000 | x | + | 3 70 | ( | 3000 | − | x | ) |
| = | 1800 | − | 11 20 | x | + | x | × | 1 30000 | x | + | 3 70 | × | 3000 | − | 3 70 | x |
| = | 1800 | − | 11 20 | x | + | x | × | 1 30000 | x | + | 900 7 | − | 3 70 | x |
| = | 13500 7 | − | 83 140 | x | + | x | × | 1 30000 | x |
13500 7 | − | 83 140 | x | + | x | × | 1 30000 | x | = | x | − | 1 20 | × | 3000 |
| 方程右边 = | x | − | 150 |
13500 7 | − | 83 140 | x | + | x | × | 1 30000 | x | = | x | − | 150 |