| ( | 428 | − | 2 | X | ) | ( | X | − | 190 | ) | = | 280 |
| 方程左边 = | 428 | ( | X | − | 190 | ) | − | 2 | X | ( | X | − | 190 | ) |
| = | 428 | X | − | 428 | × | 190 | − | 2 | X | ( | X | − | 190 | ) |
| = | 428 | X | − | 81320 | − | 2 | X | ( | X | − | 190 | ) |
| = | 428 | X | − | 81320 | − | 2 | X | X | + | 2 | X | × | 190 |
| = | 428 | X | − | 81320 | − | 2 | X | X | + | 380 | X |
| = | 808 | X | − | 81320 | − | 2 | X | X |
| 808 | X | − | 81320 | − | 2 | X | X | = | 280 |