| ( | 72 5 | + | x | ) | ÷ | ( | 180 | + | x | ) | = | 1 10 |
| 方程两边同时乘以: | ( | 180 | + | x | ) |
| ( | 72 5 | + | x | ) | = | 1 10 | ( | 180 | + | x | ) |
72 5 | + | x | = | 1 10 | ( | 180 | + | x | ) |
72 5 | + | x | = | 1 10 | × | 180 | + | 1 10 | x |
72 5 | + | x | = | 18 | + | 1 10 | x |
| x | − | 1 10 | x | = | 18 | − | 72 5 |
9 10 | x | = | 18 | − | 72 5 |
9 10 | x | = | 18 5 |
| x | = | 18 5 | ÷ | 9 10 |
| = | 18 5 | × | 10 9 |
| = | 2 | × | 2 |
| x | = | 4 |