| 400 | ( | 1 | − | X | ) | ( | 1 | − | X | ) | = | 256 |
| 方程左边 = | 400 | × | 1 | ( | 1 | − | X | ) | − | 400 | X | ( | 1 | − | X | ) |
| = | 400 | ( | 1 | − | X | ) | − | 400 | X | ( | 1 | − | X | ) |
| = | 400 | × | 1 | − | 400 | X | − | 400 | X | ( | 1 | − | X | ) |
| = | 400 | − | 400 | X | − | 400 | X | ( | 1 | − | X | ) |
| = | 400 | − | 400 | X | − | 400 | X | × | 1 | + | 400 | X | X |
| = | 400 | − | 400 | X | − | 400 | X | + | 400 | X | X |
| = | 400 | − | 800 | X | + | 400 | X | X |
| 400 | − | 800 | X | + | 400 | X | X | = | 256 |
| X1= | 1 5 |
| X2= | 9 5 |