| ( | 12 | − | y | ) | ( | 28 | − | 2 | y | ) | ÷ | 2 | = | 130 |
| 方程左边 = | 12 | ( | 28 | − | 2 | y | ) | × | 1 2 | − | y | ( | 28 | − | 2 | y | ) | × | 1 2 |
| = | 6 | ( | 28 | − | 2 | y | ) | − | y | ( | 28 | − | 2 | y | ) | × | 1 2 |
| = | 6 | × | 28 | − | 6 | × | 2 | y | − | y | ( | 28 | − | 2 | y | ) | × | 1 2 |
| = | 168 | − | 12 | y | − | y | ( | 28 | − | 2 | y | ) | × | 1 2 |
| = | 168 | − | 12 | y | − | y | × | 28 | × | 1 2 | + | y | × | 2 | y | × | 1 2 |
| = | 168 | − | 12 | y | − | y | × | 14 | + | y | × | 1 | y |
| = | 168 | − | 26 | y | + | y | × | 1 | y |
| 168 | − | 26 | y | + | y | × | 1 | y | = | 130 |