| ( | 60 | − | 2 | x | ) | ( | 60 | − | 2 | x | ) | x | = | 0 |
| 方程左边 = | 60 | ( | 60 | − | 2 | x | ) | x | − | 2 | x | ( | 60 | − | 2 | x | ) | x |
| = | 60 | × | 60 | x | − | 60 | × | 2 | x | x | − | 2 | x | ( | 60 | − | 2 | x | ) | x |
| = | 3600 | x | − | 120 | x | x | − | 2 | x | ( | 60 | − | 2 | x | ) | x |
| = | 3600 | x | − | 120 | x | x | − | 2 | x | × | 60 | x | + | 2 | x | × | 2 |
| = | 3600 | x | − | 120 | x | x | − | 120 | x | x | + | 4 | x | x | x |
| 3600 | x | − | 120 | x | x | − | 120 | x | x | + | 4 | x | x | x | = | 0 |