| x | ( | 3 | − | x | ) | × | 3 | x | ( | x | + | 3 | ) | = | 0 |
| 方程左边 = | x | × | 3 | × | 3 | x | ( | x | + | 3 | ) | − | x | x | × | 3 | x | ( | x | + | 3 | ) |
| = | x | × | 9 | x | ( | x | + | 3 | ) | − | x | x | × | 3 | x | ( | x | + | 3 | ) |
| = | x | × | 9 | x | x | + | x | × | 9 | x | × | 3 | − | x | x | × | 3 | x |
| = | x | × | 9 | x | x | + | x | × | 27 | x | − | x | x | × | 3 | x | ( | x | + | 3 | ) |
| = | x | × | 9 | x | x | + | x | × | 27 | x | − | x | x | × | 3 | x | x |
| = | x | × | 9 | x | x | + | x | × | 27 | x | − | x | x | × | 3 | x | x |
| x | × | 9 | x | x | + | x | × | 27 | x | − | x | x | × | 3 | x | x | = | 0 |