| 2 | ( | 2 | x | + | 100 | ) | = | 4 | ( | - | 4 | x | + | 200 | ) |
| 方程左边 = | 2 | × | 2 | x | + | 2 | × | 100 |
| = | 4 | x | + | 200 |
| 4 | x | + | 200 | = | 4 | ( | - | 4 | x | + | 200 | ) |
| 方程右边 = | - | 4 | × | 4 | x | + | 4 | × | 200 |
| = | - | 16 | x | + | 800 |
| 4 | x | + | 200 | = | - | 16 | x | + | 800 |
| 4 | x | + | 16 | x | = | 800 | − | 200 |
| 20 | x | = | 800 | − | 200 |
| 20 | x | = | 600 |
| x | = | 600 | ÷ | 20 |
| = | 600 | × | 1 20 |
| = | 30 | × | 1 |
| x | = | 30 |