| ( | 28 | − | 3 | x | ) | ( | 28 | − | 3 | x | ) | − | ( | 28 | − | 4 | x | ) | ( | 28 | − | 4 | x | ) | = | 2 | x |
| 方程左边 = | 28 | ( | 28 | − | 3 | x | ) | − | 3 | x | ( | 28 | − | 3 | x | ) | − | ( | 28 | − | 4 | x | ) | ( | 28 | − | 4 | x | ) |
| = | 28 | × | 28 | − | 28 | × | 3 | x | − | 3 | x | ( | 28 | − | 3 | x | ) | − | ( | 28 | − | 4 | x | ) | ( | 28 | − | 4 | x | ) |
| = | 784 | − | 84 | x | − | 3 | x | ( | 28 | − | 3 | x | ) | − | ( | 28 | − | 4 | x | ) | ( | 28 | − | 4 | x | ) |
| = | 784 | − | 84 | x | − | 3 | x | × | 28 | + | 3 | x | × | 3 | x | − | ( | 28 | − | 4 | x | ) | ( | 28 | − | 4 | x | ) |
| = | 784 | − | 84 | x | − | 84 | x | + | 9 | x | x | − | ( | 28 | − | 4 | x | ) | ( | 28 | − | 4 | x | ) |
| = | 784 | − | 168 | x | + | 9 | x | x | − | ( | 28 | − | 4 | x | ) | ( | 28 | − | 4 | x | ) |
| = | 784 | − | 168 | x | + | 9 | x | x | − | 28 | ( | 28 | − | 4 | x | ) | + | 4 | x | ( | 28 | − | 4 | x | ) |
| = | 784 | − | 168 | x | + | 9 | x | x | − | 28 | × | 28 | + | 28 | × | 4 | x | + | 4 |
| = | 784 | − | 168 | x | + | 9 | x | x | − | 784 | + | 112 | x | + | 4 | x | ( | 28 | − | 4 | x | ) |
| = | 0 | − | 56 | x | + | 9 | x | x | + | 4 | x | ( | 28 | − | 4 | x | ) |
| = | - | 56 | x | + | 9 | x | x | + | 4 | x | × | 28 | − | 4 | x | × | 4 | x |
| = | - | 56 | x | + | 9 | x | x | + | 112 | x | − | 16 | x | x |
| = | 56 | x | + | 9 | x | x | − | 16 | x | x |
| 56 | x | + | 9 | x | x | − | 16 | x | x | = | 2 | x |
| x2= | 54 7 |