| ( | 5 4 | y | − | 5 | ) | × | 10 | = | ( | y | − | 10 | ) | × | 9 |
| 方程左边 = | 5 4 | y | × | 10 | − | 5 | × | 10 |
| = | 25 2 | y | − | 50 |
25 2 | y | − | 50 | = | ( | y | − | 10 | ) | × | 9 |
| 方程右边 = | y | × | 9 | − | 10 | × | 9 |
| = | y | × | 9 | − | 90 |
25 2 | y | − | 50 | = | 9 | y | − | 90 |
25 2 | y | − | 9 | y | = | - | 90 | + | 50 |
7 2 | y | = | - | 90 | + | 50 |
7 2 | y | = | - | 40 |
| y | = | - | 40 | ÷ | 7 2 |
| = | - | 40 | × | 2 7 |
| y | = | - | 80 7 |
| y | = | - 11.428571 |