| ( | 400 | − | 240 | − | 10 | x | ) | ( | 200 | + | 40 | x | ) | = | 41600 |
| 方程左边 = | 400 | ( | 200 | + | 40 | x | ) | − | 240 | ( | 200 | + | 40 | x | ) | − | 10 | x | ( | 200 | + | 40 | x | ) |
| = | 400 | × | 200 | + | 400 | × | 40 | x | − | 240 | ( | 200 | + | 40 | x | ) | − | 10 | x | ( | 200 | + | 40 | x | ) |
| = | 80000 | + | 16000 | x | − | 240 | ( | 200 | + | 40 | x | ) | − | 10 | x | ( | 200 | + | 40 | x | ) |
| = | 80000 | + | 16000 | x | − | 240 | × | 200 | − | 240 | × | 40 | x | − | 10 | x | ( | 200 | + | 40 | x | ) |
| = | 80000 | + | 16000 | x | − | 48000 | − | 9600 | x | − | 10 | x | ( | 200 | + | 40 | x | ) |
| = | 32000 | + | 6400 | x | − | 10 | x | ( | 200 | + | 40 | x | ) |
| = | 32000 | + | 6400 | x | − | 10 | x | × | 200 | − | 10 | x | × | 40 | x |
| = | 32000 | + | 6400 | x | − | 2000 | x | − | 400 | x | x |
| = | 32000 | + | 4400 | x | − | 400 | x | x |
| 32000 | + | 4400 | x | − | 400 | x | x | = | 41600 |