| ( | ( | 3 | ÷ | 7 | ) | r | + | 10 | ) | ÷ | ( | 30 | + | r | ) | = | 4 | ÷ | 3 |
| 方程两边同时乘以: | ( | 30 | + | r | ) |
| ( | ( | 3 | ÷ | 7 | ) | r | + | 10 | ) | = | 4 | ÷ | 3 | × | ( | 30 | + | r | ) |
| ( | 3 | ÷ | 7 | ) | r | + | 10 | = | 4 | ÷ | 3 | × | ( | 30 | + | r | ) |
| ( | 3 | ÷ | 7 | ) | r | + | 10 | = | 4 | ÷ | 3 | × | 30 | + | 4 | ÷ | 3 | × | r |
| ( | 3 | ÷ | 7 | ) | r | + | 10 | = | 40 | + | 4 3 | r |
| 3 | ÷ | 7 | × | r | + | 10 | = | 40 | + | 4 3 | r |
3 7 | r | + | 10 | = | 40 | + | 4 3 | r |
3 7 | r | − | 4 3 | r | = | 40 | − | 10 |
| - | 19 21 | r | = | 40 | − | 10 |
| - | 19 21 | r | = | 30 |
| - | 30 | = | 19 21 | r |
19 21 | r | = | - | 30 |
| r | = | - | 30 | ÷ | 19 21 |
| = | - | 30 | × | 21 19 |
| r | = | - | 630 19 |
| r | = | - 33.157895 |