| x | ( | x | + | 1 | ) | ÷ | 2 | − | x | ( | x | − | 1 | ) | ÷ | 2 | = | 20 |
| 方程左边 = | x | x | × | 1 2 | + | x | × | 1 | × | 1 2 | − | x | ( | x | − | 1 | ) | × | 1 2 |
| = | x | x | × | 1 2 | + | x | × | 1 2 | − | x | ( | x | − | 1 | ) | × | 1 2 |
| = | x | x | × | 1 2 | + | 1 2 | x | − | x | x | × | 1 2 | + | x | × | 1 | × | 1 2 |
| = | x | x | × | 1 2 | + | 1 2 | x | − | x | x | × | 1 2 | + | x | × | 1 2 |
| = | x | x | × | 1 2 | + | 1 | x | − | x | x | × | 1 2 |
| x | x | × | 1 2 | + | 1 | x | − | x | x | × | 1 2 | = | 20 |