| 20 | X | ( | 14 5 | + | 1 5 | ) | + | ( | 19 5 | + | 1 5 | ) | X | ( | X | − | 20 | ) | = | 80 |
| 方程左边 = | 20 | X | × | 14 5 | + | 20 | X | × | 1 5 | + | ( | 19 5 | + | 1 5 | ) | X | ( | X | − | 20 | ) |
| = | 56 | X | + | 4 | X | + | ( | 19 5 | + | 1 5 | ) | X | ( | X | − | 20 | ) |
| = | 60 | X | + | ( | 19 5 | + | 1 5 | ) | X | ( | X | − | 20 | ) |
| = | 60 | X | + | 19 5 | X | ( | X | − | 20 | ) | + | 1 5 | X | ( | X | − | 20 | ) |
| = | 60 | X | + | 19 5 | X | X | − | 19 5 | X | × | 20 | + | 1 5 | X | ( | X | − | 20 | ) |
| = | 60 | X | + | 19 5 | X | X | − | 76 | X | + | 1 5 | X | ( | X | − | 20 | ) |
| = | - | 16 | X | + | 19 5 | X | X | + | 1 5 | X | ( | X | − | 20 | ) |
| = | - | 16 | X | + | 19 5 | X | X | + | 1 5 | X | X | − | 1 5 | X | × | 20 |
| = | - | 16 | X | + | 19 5 | X | X | + | 1 5 | X | X | − | 4 | X |
| = | - | 20 | X | + | 19 5 | X | X | + | 1 5 | X | X |
| - | 20 | X | + | 19 5 | X | X | + | 1 5 | X | X | = | 80 |