| ( | 4 | x | − | 1 | ) | ( | 5 | x | + | 7 | ) | = | 0 |
| 方程左边 = | 4 | x | ( | 5 | x | + | 7 | ) | − | 1 | ( | 5 | x | + | 7 | ) |
| = | 4 | x | × | 5 | x | + | 4 | x | × | 7 | − | 1 | ( | 5 | x | + | 7 | ) |
| = | 20 | x | x | + | 28 | x | − | 1 | ( | 5 | x | + | 7 | ) |
| = | 20 | x | x | + | 28 | x | − | 1 | × | 5 | x | − | 1 | × | 7 |
| = | 20 | x | x | + | 28 | x | − | 5 | x | − | 7 |
| = | 20 | x | x | + | 23 | x | − | 7 |
| 20 | x | x | + | 23 | x | − | 7 | = | 0 |
| x1= | - | 7 5 |
| x2= | 1 4 |