| ( | 40 | − | x | − | 30 | ) | ( | 48 | + | 8 | x | ) | = | 504 |
| 方程左边 = | 40 | ( | 48 | + | 8 | x | ) | − | x | ( | 48 | + | 8 | x | ) | − | 30 | ( | 48 | + | 8 | x | ) |
| = | 40 | × | 48 | + | 40 | × | 8 | x | − | x | ( | 48 | + | 8 | x | ) | − | 30 | ( | 48 | + | 8 | x | ) |
| = | 1920 | + | 320 | x | − | x | ( | 48 | + | 8 | x | ) | − | 30 | ( | 48 | + | 8 | x | ) |
| = | 1920 | + | 320 | x | − | x | × | 48 | − | x | × | 8 | x | − | 30 | ( | 48 | + | 8 | x | ) |
| = | 1920 | + | 272 | x | − | x | × | 8 | x | − | 30 | ( | 48 | + | 8 | x | ) |
| = | 1920 | + | 272 | x | − | x | × | 8 | x | − | 30 | × | 48 | − | 30 | × | 8 | x |
| = | 1920 | + | 272 | x | − | x | × | 8 | x | − | 1440 | − | 240 | x |
| = | 480 | + | 32 | x | − | x | × | 8 | x |
| 480 | + | 32 | x | − | x | × | 8 | x | = | 504 |