| 400 | x | ( | 1 | − | x | ) | ( | 1 | − | x | ) | = | 324 |
| 方程左边 = | 400 | x | × | 1 | ( | 1 | − | x | ) | − | 400 | x | x | ( | 1 | − | x | ) |
| = | 400 | x | ( | 1 | − | x | ) | − | 400 | x | x | ( | 1 | − | x | ) |
| = | 400 | x | × | 1 | − | 400 | x | x | − | 400 | x | x | ( | 1 | − | x | ) |
| = | 400 | x | − | 400 | x | x | − | 400 | x | x | ( | 1 | − | x | ) |
| = | 400 | x | − | 400 | x | x | − | 400 | x | x | × | 1 | + | 400 | x | x |
| = | 400 | x | − | 400 | x | x | − | 400 | x | x | + | 400 | x | x | x |
| 400 | x | − | 400 | x | x | − | 400 | x | x | + | 400 | x | x | x | = | 324 |