| x | x | x | x | = | ( | 9 | − | x | x | ) | ( | 7 | − | x | ) | ( | 7 | − | x | ) |
| 方程右边 = | 9 | ( | 7 | − | x | ) | ( | 7 | − | x | ) | − | x | x | ( | 7 | − | x | ) | ( | 7 | − | x | ) |
| = | 9 | × | 7 | ( | 7 | − | x | ) | − | 9 | x | ( | 7 | − | x | ) | − | x | x | ( | 7 | − | x | ) | ( | 7 | − | x | ) |
| = | 63 | ( | 7 | − | x | ) | − | 9 | x | ( | 7 | − | x | ) | − | x | x | ( | 7 | − | x | ) | ( | 7 | − | x | ) |
| = | 63 | × | 7 | − | 63 | x | − | 9 | x | ( | 7 | − | x | ) | − | x | x | ( | 7 | − | x | ) | ( | 7 | − | x | ) |
| = | 441 | − | 63 | x | − | 9 | x | ( | 7 | − | x | ) | − | x | x | ( | 7 | − | x | ) | ( | 7 | − | x | ) |
| = | 441 | − | 63 | x | − | 9 | x | × | 7 | + | 9 | x | x | − | x | x | ( | 7 | − | x | ) |
| = | 441 | − | 63 | x | − | 63 | x | + | 9 | x | x | − | x | x | ( | 7 | − | x | ) | ( | 7 | − | x | ) |
| = | 441 | − | 126 | x | + | 9 | x | x | − | x | x | ( | 7 | − | x | ) | ( | 7 | − | x | ) |
| = | 441 | − | 126 | x | + | 9 | x | x | − | x | x | × | 7 | ( | 7 | − | x | ) | + | x | x |
| = | 441 | − | 126 | x | + | 9 | x | x | − | x | x | × | 7 | × | 7 | + | x | x |
| = | 441 | − | 126 | x | + | 9 | x | x | − | x | x | × | 49 | + | x | x | × | 7 |
| = | 441 | − | 126 | x | + | 9 | x | x | − | x | x | × | 49 | + | x | x | × | 7 |
| x | x | x | x | = | 441 | − | 126 | x | + | 9 | x | x | − | x | x | × | 49 | + | x | x | × | 7 |