| ( | 10 | − | 2 | a | ) | ( | 10 | − | 2 | a | ) | = | 0 |
| 方程左边 = | 10 | ( | 10 | − | 2 | a | ) | − | 2 | a | ( | 10 | − | 2 | a | ) |
| = | 10 | × | 10 | − | 10 | × | 2 | a | − | 2 | a | ( | 10 | − | 2 | a | ) |
| = | 100 | − | 20 | a | − | 2 | a | ( | 10 | − | 2 | a | ) |
| = | 100 | − | 20 | a | − | 2 | a | × | 10 | + | 2 | a | × | 2 | a |
| = | 100 | − | 20 | a | − | 20 | a | + | 4 | a | a |
| = | 100 | − | 40 | a | + | 4 | a | a |
| 100 | − | 40 | a | + | 4 | a | a | = | 0 |