| ( | 100 | + | 5 | x | ) | ( | 160 | − | x | ) | − | 100 | ( | 100 | + | 5 | x | ) | = | 7875 |
| 方程左边 = | 100 | ( | 160 | − | x | ) | + | 5 | x | ( | 160 | − | x | ) | − | 100 | ( | 100 | + | 5 | x | ) |
| = | 100 | × | 160 | − | 100 | x | + | 5 | x | ( | 160 | − | x | ) | − | 100 | ( | 100 | + | 5 | x | ) |
| = | 16000 | − | 100 | x | + | 5 | x | ( | 160 | − | x | ) | − | 100 | ( | 100 | + | 5 | x | ) |
| = | 16000 | − | 100 | x | + | 5 | x | × | 160 | − | 5 | x | x | − | 100 | ( | 100 | + | 5 | x | ) |
| = | 16000 | − | 100 | x | + | 800 | x | − | 5 | x | x | − | 100 | ( | 100 | + | 5 | x | ) |
| = | 16000 | + | 700 | x | − | 5 | x | x | − | 100 | ( | 100 | + | 5 | x | ) |
| = | 16000 | + | 700 | x | − | 5 | x | x | − | 100 | × | 100 | − | 100 | × | 5 | x |
| = | 16000 | + | 700 | x | − | 5 | x | x | − | 10000 | − | 500 | x |
| = | 6000 | + | 200 | x | − | 5 | x | x |
| 6000 | + | 200 | x | − | 5 | x | x | = | 7875 |