3 20 | ( | x | − | 4 | ) | ( | x | − | 4 | ) | + | 3 | = | 0 |
| 方程左边 = | 3 20 | x | ( | x | − | 4 | ) | − | 3 20 | × | 4 | ( | x | − | 4 | ) | + | 3 |
| = | 3 20 | x | ( | x | − | 4 | ) | − | 3 5 | ( | x | − | 4 | ) | + | 3 |
| = | 3 20 | x | x | − | 3 20 | x | × | 4 | − | 3 5 | ( | x | − | 4 | ) | + | 3 |
| = | 3 20 | x | x | − | 3 5 | x | − | 3 5 | ( | x | − | 4 | ) | + | 3 |
| = | 3 20 | x | x | − | 3 5 | x | − | 3 5 | x | + | 3 5 | × | 4 | + | 3 |
| = | 3 20 | x | x | − | 3 5 | x | − | 3 5 | x | + | 12 5 | + | 3 |
| = | 3 20 | x | x | − | 6 5 | x | + | 27 5 |
3 20 | x | x | − | 6 5 | x | + | 27 5 | = | 0 |