| x | = | 81 | ÷ | ( | ( | 1 | ÷ | ( | 1 | ÷ | 4 | ) | ) | + | ( | 1 | ÷ | ( | 1 | ÷ | 5 | ) | ) | ) | ÷ | ( | 1 | ÷ | 5 | ) |
| 方程两边同时乘以: | ( | ( | 1 | ÷ | ( | 1 | ÷ | 4 | ) | ) | + | ( | 1 | ÷ | ( | 1 | ÷ | 5 | ) | ) | ) |
| x | ( | ( | 1 | ÷ | ( | 1 | ÷ | 4 | ) | ) | + | ( | 1 | ÷ | ( | 1 | ÷ | 5 | ) | ) | ) | = | 81 | ÷ | ( | 1 | ÷ | 5 | ) |
| x | ( | 1 | ÷ | ( | 1 | ÷ | 4 | ) | ) | + | x | ( | 1 | ÷ | ( | 1 | ÷ | 5 | ) | ) | = | 81 | ÷ | ( | 1 | ÷ | 5 | ) |
| 方程两边同时乘以: | ( | 1 | ÷ | 5 | ) |
| x | ( | 1 | ÷ | ( | 1 | ÷ | 4 | ) | ) | ( | 1 | ÷ | 5 | ) | + | x | ( | 1 | ÷ | ( | 1 | ÷ | 5 | ) | ) | ( | 1 | ÷ | 5 | ) | = | 81 |
| x | × | 1 | ÷ | ( | 1 | ÷ | 4 | ) | × | ( | 1 | ÷ | 5 | ) | + | x | ( | 1 | ÷ | ( | 1 | ÷ | 5 | ) | ) | ( | 1 | ÷ | 5 | ) | = | 81 |
| 方程两边同时乘以: | ( | 1 | ÷ | 4 | ) |
| x | × | 1 | ( | 1 | ÷ | 5 | ) | + | x | ( | 1 | ÷ | ( | 1 | ÷ | 5 | ) | ) | ( | 1 | ÷ | 5 | ) | ( | 1 | ÷ | 4 | ) | = | 81 | ( | 1 | ÷ | 4 | ) |
| x | × | 1 | × | 1 | ÷ | 5 | + | x | ( | 1 | ÷ | ( | 1 | ÷ | 5 | ) | ) | ( | 1 | ÷ | 5 | ) | ( | 1 | ÷ | 4 | ) | = | 81 | ( | 1 | ÷ | 4 | ) |
| x | × | 1 | × | 1 | ÷ | 5 | + | x | ( | 1 | ÷ | ( | 1 | ÷ | 5 | ) | ) | ( | 1 | ÷ | 5 | ) | ( | 1 | ÷ | 4 | ) | = | 81 | × | 1 | ÷ | 4 |
| x | × | 1 5 | + | x | ( | 1 | ÷ | ( | 1 | ÷ | 5 | ) | ) | ( | 1 | ÷ | 5 | ) | ( | 1 | ÷ | 4 | ) | = | 81 4 |
1 5 | x | + | x | × | 1 | ÷ | ( | 1 | ÷ | 5 | ) | × | ( | 1 | ÷ | 5 | ) | ( | 1 | ÷ | 4 | ) | = | 81 4 |
| 方程两边同时乘以: | ( | 1 | ÷ | 5 | ) |
1 5 | x | ( | 1 | ÷ | 5 | ) | + | x | × | 1 | ( | 1 | ÷ | 5 | ) | ( | 1 | ÷ | 4 | ) | = | 81 4 | ( | 1 | ÷ | 5 | ) |
1 5 | x | × | 1 | ÷ | 5 | + | x | × | 1 | ( | 1 | ÷ | 5 | ) | ( | 1 | ÷ | 4 | ) | = | 81 4 | ( | 1 | ÷ | 5 | ) |
1 5 | x | × | 1 | ÷ | 5 | + | x | × | 1 | ( | 1 | ÷ | 5 | ) | ( | 1 | ÷ | 4 | ) | = | 81 4 | × | 1 | ÷ | 5 |
1 25 | x | + | x | × | 1 | ( | 1 | ÷ | 5 | ) | ( | 1 | ÷ | 4 | ) | = | 81 20 |
1 25 | x | + | x | × | 1 | × | 1 | ÷ | 5 | × | ( | 1 | ÷ | 4 | ) | = | 81 20 |
1 25 | x | + | x | × | 1 5 | ( | 1 | ÷ | 4 | ) | = | 81 20 |
1 25 | x | + | x | × | 1 5 | × | 1 | ÷ | 4 | = | 81 20 |
1 25 | x | + | x | × | 1 20 | = | 81 20 |
9 100 | x | = | 81 20 |
| x | = | 81 20 | ÷ | 9 100 |
| = | 81 20 | × | 100 9 |
| = | 9 | × | 5 |
| x | = | 45 |