| ( | 2 | − | X | ) | ( | 30 | + | ( | 20 | X | ÷ | 1 2 | ) | ) | = | 70 |
| 方程左边 = | 2 | ( | 30 | + | ( | 20 | X | ÷ | 1 2 | ) | ) | − | X | ( | 30 | + | ( | 20 | X | ÷ | 1 2 | ) | ) |
| = | 2 | × | 30 | + | 2 | ( | 20 | X | ÷ | 1 2 | ) | − | X | ( | 30 | + | ( | 20 | X | ÷ | 1 2 | ) | ) |
| = | 60 | + | 2 | ( | 20 | X | ÷ | 1 2 | ) | − | X | ( | 30 | + | ( | 20 | X | ÷ | 1 2 | ) | ) |
| = | 60 | + | 2 | × | 20 | X | ÷ | 1 2 | − | X | ( | 30 | + | ( | 20 | X | ÷ | 1 2 | ) | ) |
| = | 60 | + | 80 | X | − | X | ( | 30 | + | ( | 20 | X | ÷ | 1 2 | ) | ) |
| = | 60 | + | 80 | X | − | X | × | 30 | − | X | ( | 20 | X | ÷ | 1 2 | ) |
| = | 60 | + | 50 | X | − | X | ( | 20 | X | ÷ | 1 2 | ) |
| = | 60 | + | 50 | X | − | X | × | 20 | X | ÷ | 1 2 |
| = | 60 | + | 50 | X | − | X | × | 40 | X |
| 60 | + | 50 | X | − | X | × | 40 | X | = | 70 |
| X1= | 1 4 |
| X2=1 |