| ( | 21 2 | + | 11 | + | 5 | x | ) | × | 3 | = | ( | 21 2 | + | 11 | + | 3 | x | ) | × | 4 |
| 方程左边 = | 21 2 | × | 3 | + | 11 | × | 3 | + | 5 | x | × | 3 |
| = | 63 2 | + | 33 | + | 15 | x |
| = | 129 2 | + | 15 | x |
129 2 | + | 15 | x | = | ( | 21 2 | + | 11 | + | 3 | x | ) | × | 4 |
| 方程右边 = | 21 2 | × | 4 | + | 11 | × | 4 | + | 3 | x | × | 4 |
| = | 42 | + | 44 | + | 12 | x |
| = | 86 | + | 12 | x |
129 2 | + | 15 | x | = | 86 | + | 12 | x |
| 15 | x | − | 12 | x | = | 86 | − | 129 2 |
| 3 | x | = | 86 | − | 129 2 |
| 3 | x | = | 43 2 |
| x | = | 43 2 | ÷ | 3 |
| = | 43 2 | × | 1 3 |
| x | = | 43 6 |
| x | = | 7.166667 |