| ( | 40 | x | − | 240 | ) | ( | 1800 | − | 160 | x | ) | = | 41600 |
| 方程左边 = | 40 | x | ( | 1800 | − | 160 | x | ) | − | 240 | ( | 1800 | − | 160 | x | ) |
| = | 40 | x | × | 1800 | − | 40 | x | × | 160 | x | − | 240 | ( | 1800 | − | 160 | x | ) |
| = | 72000 | x | − | 6400 | x | x | − | 240 | ( | 1800 | − | 160 | x | ) |
| = | 72000 | x | − | 6400 | x | x | − | 240 | × | 1800 | + | 240 | × | 160 | x |
| = | 72000 | x | − | 6400 | x | x | − | 432000 | + | 38400 | x |
| = | 110400 | x | − | 6400 | x | x | − | 432000 |
| 110400 | x | − | 6400 | x | x | − | 432000 | = | 41600 |
| x2= | 37 4 |