| ( | 3 | k | − | 13 2 | ) | ( | 7 2 | − | k | ) | = | - | 2 | k | − | 2 |
| 方程左边 = | 3 | k | ( | 7 2 | − | k | ) | − | 13 2 | ( | 7 2 | − | k | ) |
| = | 3 | k | × | 7 2 | − | 3 | k | k | − | 13 2 | ( | 7 2 | − | k | ) |
| = | 21 2 | k | − | 3 | k | k | − | 13 2 | ( | 7 2 | − | k | ) |
| = | 21 2 | k | − | 3 | k | k | − | 13 2 | × | 7 2 | + | 13 2 | k |
| = | 21 2 | k | − | 3 | k | k | − | 91 4 | + | 13 2 | k |
| = | 17 | k | − | 3 | k | k | − | 91 4 |
| 17 | k | − | 3 | k | k | − | 91 4 | = | - | 2 | k | − | 2 |