| ( | ( | 36 | ÷ | r | ) | − | r | ) | ÷ | 4 | = | ( | 2 | r | − | ( | 36 | ÷ | r | ) | ) | ÷ | 5 |
| ( | 36 | ÷ | r | ) | ÷ | 4 | − | r | ÷ | 4 | = | ( | 2 | r | − | ( | 36 | ÷ | r | ) | ) | ÷ | 5 |
| ( | 36 | ÷ | r | ) | ÷ | 4 | − | r | ÷ | 4 | = | 2 | r | ÷ | 5 | − | ( | 36 | ÷ | r | ) | ÷ | 5 |
| ( | 36 | ÷ | r | ) | × | 1 4 | − | r | × | 1 4 | = | 2 5 | r | − | ( | 36 | ÷ | r | ) | × | 1 5 |
| 36 | ÷ | r | × | 1 4 | − | 1 4 | r | = | 2 5 | r | − | ( | 36 | ÷ | r | ) | × | 1 5 |
| 36 | ÷ | r | × | 1 4 | − | 1 4 | r | = | 2 5 | r | − | 36 | ÷ | r | × | 1 5 |
| 9 | ÷ | r | − | 1 4 | r | = | 2 5 | r | − | 36 5 | ÷ | r |
| 方程两边同时乘以: | r |
| 9 | − | 1 4 | r | r | = | 2 5 | r | r | − | 36 5 | ÷ | 1 | × | 1 |