| 125000 | − | ( | ( | 400 | − | 400 | a | ) | ( | 200 | + | 200 | a | ) | + | 3000 | a | ) | = | 8750 |
| 方程左边 = | 125000 | − | ( | 400 | − | 400 | a | ) | ( | 200 | + | 200 | a | ) | − | 3000 | a |
| = | 125000 | − | 400 | ( | 200 | + | 200 | a | ) | + | 400 | a | ( | 200 | + | 200 | a | ) | − | 3000 | a |
| = | 125000 | − | 400 | × | 200 | − | 400 | × | 200 | a | + | 400 | a | ( | 200 | + | 200 | a | ) | − | 3000 | a |
| = | 125000 | − | 80000 | − | 80000 | a | + | 400 | a | ( | 200 | + | 200 | a | ) | − | 3000 | a |
| = | 45000 | − | 83000 | a | + | 400 | a | ( | 200 | + | 200 | a | ) |
| = | 45000 | − | 83000 | a | + | 400 | a | × | 200 | + | 400 | a | × | 200 | a |
| = | 45000 | − | 83000 | a | + | 80000 | a | + | 80000 | a | a |
| = | 45000 | − | 3000 | a | + | 80000 | a | a |
| 45000 | − | 3000 | a | + | 80000 | a | a | = | 8750 |