| ( | 20 | − | x | ) | ( | 49 5 | − | x | ) | − | 49 5 | x | = | 0 |
| 方程左边 = | 20 | ( | 49 5 | − | x | ) | − | x | ( | 49 5 | − | x | ) | − | 49 5 | x |
| = | 20 | × | 49 5 | − | 20 | x | − | x | ( | 49 5 | − | x | ) | − | 49 5 | x |
| = | 196 | − | 20 | x | − | x | ( | 49 5 | − | x | ) | − | 49 5 | x |
| = | 196 | − | 149 5 | x | − | x | ( | 49 5 | − | x | ) |
| = | 196 | − | 149 5 | x | − | x | × | 49 5 | + | x | x |
| = | 196 | − | 198 5 | x | + | x | x |
| 196 | − | 198 5 | x | + | x | x | = | 0 |