| ( | 40 | + | 40 | − | 1 2 | X | ) | ( | X | ÷ | 2 | ) | = | 200 |
| 方程左边 = | 40 | ( | X | ÷ | 2 | ) | + | 40 | ( | X | ÷ | 2 | ) | − | 1 2 | X | ( | X | ÷ | 2 | ) |
| = | 40 | X | ÷ | 2 | + | 40 | ( | X | ÷ | 2 | ) | − | 1 2 | X | ( | X | ÷ | 2 | ) |
| = | 20 | X | + | 40 | ( | X | ÷ | 2 | ) | − | 1 2 | X | ( | X | ÷ | 2 | ) |
| = | 20 | X | + | 40 | X | ÷ | 2 | − | 1 2 | X | ( | X | ÷ | 2 | ) |
| = | 20 | X | + | 20 | X | − | 1 2 | X | ( | X | ÷ | 2 | ) |
| = | 40 | X | − | 1 2 | X | ( | X | ÷ | 2 | ) |
| = | 40 | X | − | 1 2 | X | X | ÷ | 2 |
| = | 40 | X | − | 1 4 | X | X |
| 40 | X | − | 1 4 | X | X | = | 200 |