| 108 | + | ( | k | − | 30 | + | k | ) | × | 18 5 | = | 72 | + | ( | k | − | 30 | + | k | ) | × | 12 5 |
| 方程左边 = | 108 | + | k | × | 18 5 | − | 30 | × | 18 5 | + | k | × | 18 5 |
| = | 108 | + | k | × | 18 5 | − | 108 | + | k | × | 18 5 |
| = | 0 | + | 36 5 | k |
36 5 | k | = | 72 | + | ( | k | − | 30 | + | k | ) | × | 12 5 |
| 方程右边 = | 72 | + | k | × | 12 5 | − | 30 | × | 12 5 | + | k | × | 12 5 |
| = | 72 | + | k | × | 12 5 | − | 72 | + | k | × | 12 5 |
| = | 0 | + | 24 5 | k |
36 5 | k | = | 0 | + | 24 5 | k |
36 5 | k | − | 24 5 | k | = | 0 |
12 5 | k | = | 0 |
| k | = | 0 | ÷ | 12 5 |
| = | 0 | × | 5 12 |
| k | = | 0 |