| 3 | x | ( | 2 | − | 6 | ) | ( | 12 | + | 36 | ) | = | 72 |
| 方程左边 = | 3 | x | × | 2 | ( | 12 | + | 36 | ) | − | 3 | x | × | 6 | ( | 12 | + | 36 | ) |
| = | 6 | x | ( | 12 | + | 36 | ) | − | 18 | x | ( | 12 | + | 36 | ) |
| = | 6 | x | × | 12 | + | 6 | x | × | 36 | − | 18 | x | ( | 12 | + | 36 | ) |
| = | 72 | x | + | 216 | x | − | 18 | x | ( | 12 | + | 36 | ) |
| = | 288 | x | − | 18 | x | ( | 12 | + | 36 | ) |
| = | 288 | x | − | 18 | x | × | 12 | − | 18 | x | × | 36 |
| = | 288 | x | − | 216 | x | − | 648 | x |
| = | - | 576 | x |
| - | 576 | x | = | 72 |
| - | 72 | = | 576 | x |
| 576 | x | = | - | 72 |
| x | = | - | 72 | ÷ | 576 |
| = | - | 72 | × | 1 576 |
| = | - | 1 | × | 1 8 |
| x | = | - | 1 8 |
| x | = | - 0.125 |