| ( | 3 10 | − | 1 100 | X | ) | ( | 500 | + | 40 | X | ) | = | 180 |
| 方程左边 = | 3 10 | ( | 500 | + | 40 | X | ) | − | 1 100 | X | ( | 500 | + | 40 | X | ) |
| = | 3 10 | × | 500 | + | 3 10 | × | 40 | X | − | 1 100 | X | ( | 500 | + | 40 | X | ) |
| = | 150 | + | 12 | X | − | 1 100 | X | ( | 500 | + | 40 | X | ) |
| = | 150 | + | 12 | X | − | 1 100 | X | × | 500 | − | 1 100 | X | × | 40 | X |
| = | 150 | + | 12 | X | − | 5 | X | − | 2 5 | X | X |
| = | 150 | + | 7 | X | − | 2 5 | X | X |
| 150 | + | 7 | X | − | 2 5 | X | X | = | 180 |
| X1= | 15 2 |
| X2=10 |