| 60 | ( | 1 | − | x | ) | ( | 1 | − | x | ) | = | 0 |
| 方程左边 = | 60 | × | 1 | ( | 1 | − | x | ) | − | 60 | x | ( | 1 | − | x | ) |
| = | 60 | ( | 1 | − | x | ) | − | 60 | x | ( | 1 | − | x | ) |
| = | 60 | × | 1 | − | 60 | x | − | 60 | x | ( | 1 | − | x | ) |
| = | 60 | − | 60 | x | − | 60 | x | ( | 1 | − | x | ) |
| = | 60 | − | 60 | x | − | 60 | x | × | 1 | + | 60 | x | x |
| = | 60 | − | 60 | x | − | 60 | x | + | 60 | x | x |
| = | 60 | − | 120 | x | + | 60 | x | x |
| 60 | − | 120 | x | + | 60 | x | x | = | 0 |