| ( | 100 | − | 2 | a | ) | ( | 50 | − | 2 | a | ) | = | 4704 |
| 方程左边 = | 100 | ( | 50 | − | 2 | a | ) | − | 2 | a | ( | 50 | − | 2 | a | ) |
| = | 100 | × | 50 | − | 100 | × | 2 | a | − | 2 | a | ( | 50 | − | 2 | a | ) |
| = | 5000 | − | 200 | a | − | 2 | a | ( | 50 | − | 2 | a | ) |
| = | 5000 | − | 200 | a | − | 2 | a | × | 50 | + | 2 | a | × | 2 | a |
| = | 5000 | − | 200 | a | − | 100 | a | + | 4 | a | a |
| = | 5000 | − | 300 | a | + | 4 | a | a |
| 5000 | − | 300 | a | + | 4 | a | a | = | 4704 |