| ( | x | − | 50 | ) | ( | 80 | − | x | ) | + | ( | x | − | 50 | ) | × | 160 | = | 0 |
| 方程左边 = | x | ( | 80 | − | x | ) | − | 50 | ( | 80 | − | x | ) | + | ( | x | − | 50 | ) | × | 160 |
| = | x | × | 80 | − | x | x | − | 50 | ( | 80 | − | x | ) | + | ( | x | − | 50 | ) | × | 160 |
| = | 80 | x | − | x | x | − | 50 | × | 80 | + | 50 | x | + | ( | x | − | 50 | ) | × | 160 |
| = | 80 | x | − | x | x | − | 4000 | + | 50 | x | + | ( | x | − | 50 | ) | × | 160 |
| = | 130 | x | − | x | x | − | 4000 | + | ( | x | − | 50 | ) | × | 160 |
| = | 130 | x | − | x | x | − | 4000 | + | x | × | 160 | − | 50 | × | 160 |
| = | 130 | x | − | x | x | − | 4000 | + | x | × | 160 | − | 8000 |
| = | 290 | x | − | x | x | − | 12000 |
| 290 | x | − | x | x | − | 12000 | = | 0 |