| ( | x | − | 25 | ) | ( | 37 | − | x | ) | × | 2 | = | 90 |
| 方程左边 = | x | ( | 37 | − | x | ) | × | 2 | − | 25 | ( | 37 | − | x | ) | × | 2 |
| = | x | ( | 37 | − | x | ) | × | 2 | − | 50 | ( | 37 | − | x | ) |
| = | x | × | 37 | × | 2 | − | x | x | × | 2 | − | 50 | ( | 37 | − | x | ) |
| = | x | × | 74 | − | x | x | × | 2 | − | 50 | ( | 37 | − | x | ) |
| = | 74 | x | − | x | x | × | 2 | − | 50 | × | 37 | + | 50 | x |
| = | 74 | x | − | x | x | × | 2 | − | 1850 | + | 50 | x |
| = | 124 | x | − | x | x | × | 2 | − | 1850 |
| 124 | x | − | x | x | × | 2 | − | 1850 | = | 90 |