| 400 | ( | 1 | + | x | ) | ( | 1 | + | x | ) | = | 676 |
| 方程左边 = | 400 | × | 1 | ( | 1 | + | x | ) | + | 400 | x | ( | 1 | + | x | ) |
| = | 400 | ( | 1 | + | x | ) | + | 400 | x | ( | 1 | + | x | ) |
| = | 400 | × | 1 | + | 400 | x | + | 400 | x | ( | 1 | + | x | ) |
| = | 400 | + | 400 | x | + | 400 | x | ( | 1 | + | x | ) |
| = | 400 | + | 400 | x | + | 400 | x | × | 1 | + | 400 | x | x |
| = | 400 | + | 400 | x | + | 400 | x | + | 400 | x | x |
| = | 400 | + | 800 | x | + | 400 | x | x |
| 400 | + | 800 | x | + | 400 | x | x | = | 676 |
| x1= | - | 23 10 |
| x2= | 3 10 |