| ( | X | − | 4901 20 | ) | ( | 1280 | − | X | ) | = | ( | X | − | 820 | ) | ( | 3139 10 | − | X | ) |
| 方程左边 = | X | ( | 1280 | − | X | ) | − | 4901 20 | ( | 1280 | − | X | ) |
| = | X | × | 1280 | − | X | X | − | 4901 20 | ( | 1280 | − | X | ) |
| = | 1280 | X | − | X | X | − | 4901 20 | × | 1280 | + | 4901 20 | X |
| = | 1280 | X | − | X | X | − | 313664 | + | 4901 20 | X |
| = | 30501 20 | X | − | X | X | − | 313664 |
30501 20 | X | − | X | X | − | 313664 | = | ( | X | − | 820 | ) | ( | 3139 10 | − | X | ) |
| 方程右边 = | X | ( | 3139 10 | − | X | ) | − | 820 | ( | 3139 10 | − | X | ) |
| = | X | × | 3139 10 | − | X | X | − | 820 | ( | 3139 10 | − | X | ) |
| = | 3139 10 | X | − | X | X | − | 820 | × | 3139 10 | + | 820 | X |
| = | 3139 10 | X | − | X | X | − | 257398 | + | 820 | X |
| = | 11339 10 | X | − | X | X | − | 257398 |
30501 20 | X | − | X | X | − | 313664 | = | 11339 10 | X | − | X | X | − | 257398 |