| ( | 81 | − | ( | 2 | ( | 84 | − | 81 | ) | ) | ) | ÷ | 5 | = | x |
| 方程左边 = | 81 | × | 1 5 | − | ( | 2 | ( | 84 | − | 81 | ) | ) | × | 1 5 |
| = | 81 5 | − | ( | 2 | ( | 84 | − | 81 | ) | ) | × | 1 5 |
| = | 81 5 | − | 2 | ( | 84 | − | 81 | ) | × | 1 5 |
| = | 81 5 | − | 2 5 | ( | 84 | − | 81 | ) |
| = | 81 5 | − | 2 5 | × | 84 | + | 2 5 | × | 81 |
| = | 81 5 | − | 168 5 | + | 162 5 |
| = | 15 |
| 15 | = | x |
| - | x | = | - | 15 |
| 15 | = | x |
| x | = | 15 |