| 2 | ( | ( | 30 | − | 2 | x | ) | x | + | ( | 20 | − | 2 | x | ) | x | ) | = | 200 |
| 方程左边 = | 2 | ( | 30 | − | 2 | x | ) | x | + | 2 | ( | 20 | − | 2 | x | ) | x |
| = | 2 | × | 30 | x | − | 2 | × | 2 | x | x | + | 2 | ( | 20 | − | 2 | x | ) | x |
| = | 60 | x | − | 4 | x | x | + | 2 | ( | 20 | − | 2 | x | ) | x |
| = | 60 | x | − | 4 | x | x | + | 2 | × | 20 | x | − | 2 | × | 2 | x | x |
| = | 60 | x | − | 4 | x | x | + | 40 | x | − | 4 | x | x |
| = | 100 | x | − | 4 | x | x | − | 4 | x | x |
| 100 | x | − | 4 | x | x | − | 4 | x | x | = | 200 |
| x1= | 5 2 |
| x2=10 |