| ( | - | 1 10 | x | + | 9 | ) | ( | x | − | 40 | ) | = | 168 5 |
| 方程左边 = | - | 1 10 | x | ( | x | − | 40 | ) | + | 9 | ( | x | − | 40 | ) |
| = | - | 1 10 | x | x | + | 1 10 | x | × | 40 | + | 9 | ( | x | − | 40 | ) |
| = | - | 1 10 | x | x | + | 4 | x | + | 9 | ( | x | − | 40 | ) |
| = | - | 1 10 | x | x | + | 4 | x | + | 9 | x | − | 9 | × | 40 |
| = | - | 1 10 | x | x | + | 4 | x | + | 9 | x | − | 360 |
| = | - | 1 10 | x | x | + | 13 | x | − | 360 |
| - | 1 10 | x | x | + | 13 | x | − | 360 | = | 168 5 |