| - | 4 | ( | y | − | 2 | ) | ( | 3 | y | + | 7 | ) | = | 0 |
| 方程左边 = | - | 4 | y | ( | 3 | y | + | 7 | ) | + | 4 | × | 2 | ( | 3 | y | + | 7 | ) |
| = | - | 4 | y | ( | 3 | y | + | 7 | ) | + | 8 | ( | 3 | y | + | 7 | ) |
| = | - | 4 | y | × | 3 | y | − | 4 | y | × | 7 | + | 8 | ( | 3 | y | + | 7 | ) |
| = | - | 12 | y | y | − | 28 | y | + | 8 | ( | 3 | y | + | 7 | ) |
| = | - | 12 | y | y | − | 28 | y | + | 8 | × | 3 | y | + | 8 | × | 7 |
| = | - | 12 | y | y | − | 28 | y | + | 24 | y | + | 56 |
| = | - | 12 | y | y | − | 4 | y | + | 56 |
| - | 12 | y | y | − | 4 | y | + | 56 | = | 0 |
| y1= | - | 7 3 |
| y2=2 |