| ( | 60 | − | x | − | 43 | ) | ( | 40 | + | 20 | x | ) | = | 1440 |
| 方程左边 = | 60 | ( | 40 | + | 20 | x | ) | − | x | ( | 40 | + | 20 | x | ) | − | 43 | ( | 40 | + | 20 | x | ) |
| = | 60 | × | 40 | + | 60 | × | 20 | x | − | x | ( | 40 | + | 20 | x | ) | − | 43 | ( | 40 | + | 20 | x | ) |
| = | 2400 | + | 1200 | x | − | x | ( | 40 | + | 20 | x | ) | − | 43 | ( | 40 | + | 20 | x | ) |
| = | 2400 | + | 1200 | x | − | x | × | 40 | − | x | × | 20 | x | − | 43 | ( | 40 | + | 20 | x | ) |
| = | 2400 | + | 1160 | x | − | x | × | 20 | x | − | 43 | ( | 40 | + | 20 | x | ) |
| = | 2400 | + | 1160 | x | − | x | × | 20 | x | − | 43 | × | 40 | − | 43 | × | 20 | x |
| = | 2400 | + | 1160 | x | − | x | × | 20 | x | − | 1720 | − | 860 | x |
| = | 680 | + | 300 | x | − | x | × | 20 | x |
| 680 | + | 300 | x | − | x | × | 20 | x | = | 1440 |