| ( | 5 | − | 2 | a | ) | ( | 4 | − | 2 | a | ) | = | 20 | − | 17 4 |
| 方程左边 = | 5 | ( | 4 | − | 2 | a | ) | − | 2 | a | ( | 4 | − | 2 | a | ) |
| = | 5 | × | 4 | − | 5 | × | 2 | a | − | 2 | a | ( | 4 | − | 2 | a | ) |
| = | 20 | − | 10 | a | − | 2 | a | ( | 4 | − | 2 | a | ) |
| = | 20 | − | 10 | a | − | 2 | a | × | 4 | + | 2 | a | × | 2 | a |
| = | 20 | − | 10 | a | − | 8 | a | + | 4 | a | a |
| = | 20 | − | 18 | a | + | 4 | a | a |
| 20 | − | 18 | a | + | 4 | a | a | = | 20 | − | 17 4 |
| 方程右边 = | 63 4 |
| 20 | − | 18 | a | + | 4 | a | a | = | 63 4 |
| a1= | 1 4 |
| a2= | 17 4 |