| ( | 250 | − | 25 | x | ) | ( | 12 | + | 3 | x | ) | = | 0 |
| 方程左边 = | 250 | ( | 12 | + | 3 | x | ) | − | 25 | x | ( | 12 | + | 3 | x | ) |
| = | 250 | × | 12 | + | 250 | × | 3 | x | − | 25 | x | ( | 12 | + | 3 | x | ) |
| = | 3000 | + | 750 | x | − | 25 | x | ( | 12 | + | 3 | x | ) |
| = | 3000 | + | 750 | x | − | 25 | x | × | 12 | − | 25 | x | × | 3 | x |
| = | 3000 | + | 750 | x | − | 300 | x | − | 75 | x | x |
| = | 3000 | + | 450 | x | − | 75 | x | x |
| 3000 | + | 450 | x | − | 75 | x | x | = | 0 |