| ( | 5 | − | 1 10 | x | ) | ( | 400 | + | 10 | x | ) | = | 0 |
| 方程左边 = | 5 | ( | 400 | + | 10 | x | ) | − | 1 10 | x | ( | 400 | + | 10 | x | ) |
| = | 5 | × | 400 | + | 5 | × | 10 | x | − | 1 10 | x | ( | 400 | + | 10 | x | ) |
| = | 2000 | + | 50 | x | − | 1 10 | x | ( | 400 | + | 10 | x | ) |
| = | 2000 | + | 50 | x | − | 1 10 | x | × | 400 | − | 1 10 | x | × | 10 | x |
| = | 2000 | + | 50 | x | − | 40 | x | − | 1 | x | x |
| = | 2000 | + | 10 | x | − | 1 | x | x |
| 2000 | + | 10 | x | − | 1 | x | x | = | 0 |