| ( | 130 | − | x | ) | ( | 100 | + | 5 | x | ) | − | 100 | ( | 100 | + | 5 | x | ) | = | 300 |
| 方程左边 = | 130 | ( | 100 | + | 5 | x | ) | − | x | ( | 100 | + | 5 | x | ) | − | 100 | ( | 100 | + | 5 | x | ) |
| = | 130 | × | 100 | + | 130 | × | 5 | x | − | x | ( | 100 | + | 5 | x | ) | − | 100 | ( | 100 | + | 5 | x | ) |
| = | 13000 | + | 650 | x | − | x | ( | 100 | + | 5 | x | ) | − | 100 | ( | 100 | + | 5 | x | ) |
| = | 13000 | + | 650 | x | − | x | × | 100 | − | x | × | 5 | x | − | 100 | ( | 100 | + | 5 | x | ) |
| = | 13000 | + | 550 | x | − | x | × | 5 | x | − | 100 | ( | 100 | + | 5 | x | ) |
| = | 13000 | + | 550 | x | − | x | × | 5 | x | − | 100 | × | 100 | − | 100 | × | 5 | x |
| = | 13000 | + | 550 | x | − | x | × | 5 | x | − | 10000 | − | 500 | x |
| = | 3000 | + | 50 | x | − | x | × | 5 | x |
| 3000 | + | 50 | x | − | x | × | 5 | x | = | 300 |