| ( | 38 | − | 2 5 | m | ) | ( | 500 | + | 2 | m | ) | = | 17680 |
| 方程左边 = | 38 | ( | 500 | + | 2 | m | ) | − | 2 5 | m | ( | 500 | + | 2 | m | ) |
| = | 38 | × | 500 | + | 38 | × | 2 | m | − | 2 5 | m | ( | 500 | + | 2 | m | ) |
| = | 19000 | + | 76 | m | − | 2 5 | m | ( | 500 | + | 2 | m | ) |
| = | 19000 | + | 76 | m | − | 2 5 | m | × | 500 | − | 2 5 | m | × | 2 | m |
| = | 19000 | + | 76 | m | − | 200 | m | − | 4 5 | m | m |
| = | 19000 | − | 124 | m | − | 4 5 | m | m |
| 19000 | − | 124 | m | − | 4 5 | m | m | = | 17680 |