| ( | a | − | 290 | ) | ÷ | 410 | = | ( | a | − | 515 | ) | ÷ | 210 |
| 方程左边 = | a | × | 1 410 | − | 290 | × | 1 410 |
| = | a | × | 1 410 | − | 29 41 |
1 410 | a | − | 29 41 | = | ( | a | − | 515 | ) | ÷ | 210 |
| 方程右边 = | a | × | 1 210 | − | 515 | × | 1 210 |
| = | a | × | 1 210 | − | 103 42 |
1 410 | a | − | 29 41 | = | 1 210 | a | − | 103 42 |
1 410 | a | − | 1 210 | a | = | - | 103 42 | + | 29 41 |
| - | 2 861 | a | = | - | 103 42 | + | 29 41 |
| - | 2 861 | a | = | - | 3005 1722 |
3005 1722 | = | 2 861 | a |
2 861 | a | = | 3005 1722 |
| a | = | 3005 1722 | ÷ | 2 861 |
| = | 3005 1722 | × | 861 2 |
| = | 3005 2 | × | 1 2 |
| a | = | 3005 4 |
| a | = | 751.25 |