| ( | 1 2 | − | 1 100 | a | ) | ( | 1 10 | − | 1 20 | a | ) | = | 2 | a |
| 方程左边 = | 1 2 | ( | 1 10 | − | 1 20 | a | ) | − | 1 100 | a | ( | 1 10 | − | 1 20 | a | ) |
| = | 1 2 | × | 1 10 | − | 1 2 | × | 1 20 | a | − | 1 100 | a | ( | 1 10 | − | 1 20 | a | ) |
| = | 1 20 | − | 1 40 | a | − | 1 100 | a | ( | 1 10 | − | 1 20 | a | ) |
| = | 1 20 | − | 1 40 | a | − | 1 100 | a | × | 1 10 | + | 1 100 | a | × | 1 20 | a |
| = | 1 20 | − | 1 40 | a | − | 1 1000 | a | + | 1 2000 | a | a |
| = | 1 20 | − | 13 500 | a | + | 1 2000 | a | a |
1 20 | − | 13 500 | a | + | 1 2000 | a | a | = | 2 | a |