| ( | 12 | t | − | 6 | t | t | ) | × | 20 | = | ( | 12 | − | 12 | t | ) | ( | 12 | − | 12 | t | ) |
| 方程左边 = | 12 | t | × | 20 | − | 6 | t | t | × | 20 |
| = | 240 | t | − | 120 | t | t |
| 240 | t | − | 120 | t | t | = | ( | 12 | − | 12 | t | ) | ( | 12 | − | 12 | t | ) |
| 方程右边 = | 12 | ( | 12 | − | 12 | t | ) | − | 12 | t | ( | 12 | − | 12 | t | ) |
| = | 12 | × | 12 | − | 12 | × | 12 | t | − | 12 | t | ( | 12 | − | 12 | t | ) |
| = | 144 | − | 144 | t | − | 12 | t | ( | 12 | − | 12 | t | ) |
| = | 144 | − | 144 | t | − | 12 | t | × | 12 | + | 12 | t | × | 12 | t |
| = | 144 | − | 144 | t | − | 144 | t | + | 144 | t | t |
| = | 144 | − | 288 | t | + | 144 | t | t |
| 240 | t | − | 120 | t | t | = | 144 | − | 288 | t | + | 144 | t | t |