| ( | 100 | + | a | ) | ( | 1000 | − | 2 | a | ) | = | 122200 |
| 方程左边 = | 100 | ( | 1000 | − | 2 | a | ) | + | a | ( | 1000 | − | 2 | a | ) |
| = | 100 | × | 1000 | − | 100 | × | 2 | a | + | a | ( | 1000 | − | 2 | a | ) |
| = | 100000 | − | 200 | a | + | a | ( | 1000 | − | 2 | a | ) |
| = | 100000 | − | 200 | a | + | a | × | 1000 | − | a | × | 2 | a |
| = | 100000 | + | 800 | a | − | a | × | 2 | a |
| 100000 | + | 800 | a | − | a | × | 2 | a | = | 122200 |