1 2 | ( | 800 | − | 20 | x | ) | ( | 600 | − | 10 | x | ) | = | 5 | ÷ | 8 | × | 600 | × | 800 | ÷ | 2 |
| 方程左边 = | 1 2 | × | 800 | ( | 600 | − | 10 | x | ) | − | 1 2 | × | 20 | x | ( | 600 | − | 10 | x | ) |
| = | 400 | ( | 600 | − | 10 | x | ) | − | 10 | x | ( | 600 | − | 10 | x | ) |
| = | 400 | × | 600 | − | 400 | × | 10 | x | − | 10 | x | ( | 600 | − | 10 | x | ) |
| = | 240000 | − | 4000 | x | − | 10 | x | ( | 600 | − | 10 | x | ) |
| = | 240000 | − | 4000 | x | − | 10 | x | × | 600 | + | 10 | x | × | 10 | x |
| = | 240000 | − | 4000 | x | − | 6000 | x | + | 100 | x | x |
| = | 240000 | − | 10000 | x | + | 100 | x | x |
| 240000 | − | 10000 | x | + | 100 | x | x | = | 5 | ÷ | 8 | × | 600 | × | 800 | ÷ | 2 |
| 方程右边 = | 150000 |
| 240000 | − | 10000 | x | + | 100 | x | x | = | 150000 |