| ( | 27 | − | 7 | x | ) | ( | 27 | − | 4 | x | ) | + | 27 | − | x | = | 0 |
| 方程左边 = | 27 | ( | 27 | − | 4 | x | ) | − | 7 | x | ( | 27 | − | 4 | x | ) | + | 27 | − | x |
| = | 27 | × | 27 | − | 27 | × | 4 | x | − | 7 | x | ( | 27 | − | 4 | x | ) | + | 27 | − | x |
| = | 729 | − | 108 | x | − | 7 | x | ( | 27 | − | 4 | x | ) | + | 27 | − | x |
| = | 756 | − | 109 | x | − | 7 | x | ( | 27 | − | 4 | x | ) |
| = | 756 | − | 109 | x | − | 7 | x | × | 27 | + | 7 | x | × | 4 | x |
| = | 756 | − | 109 | x | − | 189 | x | + | 28 | x | x |
| = | 756 | − | 298 | x | + | 28 | x | x |
| 756 | − | 298 | x | + | 28 | x | x | = | 0 |