21 10 | ( | 1 | + | 1 4 | x | ) | = | 12 5 | ( | 1 | + | 1 4 | ( | x | − | 1 5 | ) | ) |
| 方程左边 = | 21 10 | × | 1 | + | 21 10 | × | 1 4 | x |
| = | 21 10 | + | 21 40 | x |
21 10 | + | 21 40 | x | = | 12 5 | ( | 1 | + | 1 4 | ( | x | − | 1 5 | ) | ) |
| 方程右边 = | 12 5 | × | 1 | + | 12 5 | × | 1 4 | ( | x | − | 1 5 | ) |
| = | 12 5 | + | 3 5 | ( | x | − | 1 5 | ) |
| = | 12 5 | + | 3 5 | x | − | 3 5 | × | 1 5 |
| = | 12 5 | + | 3 5 | x | − | 3 25 |
| = | 57 25 | + | 3 5 | x |
21 10 | + | 21 40 | x | = | 57 25 | + | 3 5 | x |
21 40 | x | − | 3 5 | x | = | 57 25 | − | 21 10 |
| - | 3 40 | x | = | 57 25 | − | 21 10 |
| - | 3 40 | x | = | 9 50 |
| - | 9 50 | = | 3 40 | x |
3 40 | x | = | - | 9 50 |
| x | = | - | 9 50 | ÷ | 3 40 |
| = | - | 9 50 | × | 40 3 |
| = | - | 3 5 | × | 4 |
| x | = | - | 12 5 |
| x | = | - 2.4 |