| 50 | ( | v | − | 3 5 | ) | ( | v | − | 3 5 | ) | = | 9 5 | − | v |
| 方程左边 = | 50 | v | ( | v | − | 3 5 | ) | − | 50 | × | 3 5 | ( | v | − | 3 5 | ) |
| = | 50 | v | ( | v | − | 3 5 | ) | − | 30 | ( | v | − | 3 5 | ) |
| = | 50 | v | v | − | 50 | v | × | 3 5 | − | 30 | ( | v | − | 3 5 | ) |
| = | 50 | v | v | − | 30 | v | − | 30 | ( | v | − | 3 5 | ) |
| = | 50 | v | v | − | 30 | v | − | 30 | v | + | 30 | × | 3 5 |
| = | 50 | v | v | − | 30 | v | − | 30 | v | + | 18 |
| = | 50 | v | v | − | 60 | v | + | 18 |
| 50 | v | v | − | 60 | v | + | 18 | = | 9 5 | − | v |