| ( | 1 5 | + | X | ) | ( | 160 | − | 200 | X | ) | = | 50 |
| 方程左边 = | 1 5 | ( | 160 | − | 200 | X | ) | + | X | ( | 160 | − | 200 | X | ) |
| = | 1 5 | × | 160 | − | 1 5 | × | 200 | X | + | X | ( | 160 | − | 200 | X | ) |
| = | 32 | − | 40 | X | + | X | ( | 160 | − | 200 | X | ) |
| = | 32 | − | 40 | X | + | X | × | 160 | − | X | × | 200 | X |
| = | 32 | + | 120 | X | − | X | × | 200 | X |
| 32 | + | 120 | X | − | X | × | 200 | X | = | 50 |
| X1= | 3 10 |
| X2= | 3 10 |