| ( | 400 | ( | x | + | 1 | ) | − | 50 | ) | ( | 1 | + | x | + | 1 40 | ) | = | 378 |
| 方程左边 = | 400 | ( | x | + | 1 | ) | ( | 1 | + | x | + | 1 40 | ) | − | 50 | ( | 1 | + | x | + | 1 40 | ) |
| = | 400 | x | ( | 1 | + | x | + | 1 40 | ) | + | 400 | × | 1 | ( | 1 | + | x | + | 1 40 | ) | − | 50 | ( | 1 | + | x | + | 1 40 | ) |
| = | 400 | x | ( | 1 | + | x | + | 1 40 | ) | + | 400 | ( | 1 | + | x | + | 1 40 | ) | − | 50 | ( | 1 | + | x | + | 1 40 | ) |
| = | 400 | x | × | 1 | + | 400 | x | x | + | 400 | x | × | 1 40 | + | 400 | ( | 1 | + | x | + | 1 40 | ) | − | 50 |
| = | 400 | x | + | 400 | x | x | + | 10 | x | + | 400 | ( | 1 | + | x | + | 1 40 | ) | − | 50 | ( | 1 | + | x | + | 1 40 | ) |
| = | 410 | x | + | 400 | x | x | + | 400 | ( | 1 | + | x | + | 1 40 | ) | − | 50 | ( | 1 | + | x | + | 1 40 | ) |
| = | 410 | x | + | 400 | x | x | + | 400 | × | 1 | + | 400 | x | + | 400 | × | 1 40 | − | 50 |
| = | 410 | x | + | 400 | x | x | + | 400 | + | 400 | x | + | 10 | − | 50 | ( | 1 | + | x | + | 1 40 | ) |
| = | 810 | x | + | 400 | x | x | + | 410 | − | 50 | ( | 1 | + | x | + | 1 40 | ) |
| = | 810 | x | + | 400 | x | x | + | 410 | − | 50 | × | 1 | − | 50 | x | − | 50 | × | 1 40 |
| = | 810 | x | + | 400 | x | x | + | 410 | − | 50 | − | 50 | x | − | 5 4 |
| = | 760 | x | + | 400 | x | x | + | 1435 4 |
| 760 | x | + | 400 | x | x | + | 1435 4 | = | 378 |
| x1= | - | 77 40 |
| x2= | 1 40 |