| ( | 68 | − | x | ) | ( | 35 | + | 2 | x | ) | + | ( | 100 | − | x | ) | ( | 15 | + | x | ) | = | 4240 |
| 方程左边 = | 68 | ( | 35 | + | 2 | x | ) | − | x | ( | 35 | + | 2 | x | ) | + | ( | 100 | − | x | ) | ( | 15 | + | x | ) |
| = | 68 | × | 35 | + | 68 | × | 2 | x | − | x | ( | 35 | + | 2 | x | ) | + | ( | 100 | − | x | ) | ( | 15 | + | x | ) |
| = | 2380 | + | 136 | x | − | x | ( | 35 | + | 2 | x | ) | + | ( | 100 | − | x | ) | ( | 15 | + | x | ) |
| = | 2380 | + | 136 | x | − | x | × | 35 | − | x | × | 2 | x | + | ( | 100 | − | x | ) | ( | 15 | + | x | ) |
| = | 2380 | + | 101 | x | − | x | × | 2 | x | + | ( | 100 | − | x | ) | ( | 15 | + | x | ) |
| = | 2380 | + | 101 | x | − | x | × | 2 | x | + | 100 | ( | 15 | + | x | ) | − | x | ( | 15 | + | x | ) |
| = | 2380 | + | 101 | x | − | x | × | 2 | x | + | 100 | × | 15 | + | 100 | x | − | x | ( | 15 | + | x | ) |
| = | 2380 | + | 101 | x | − | x | × | 2 | x | + | 1500 | + | 100 | x | − | x | ( | 15 | + | x | ) |
| = | 3880 | + | 201 | x | − | x | × | 2 | x | − | x | ( | 15 | + | x | ) |
| = | 3880 | + | 201 | x | − | x | × | 2 | x | − | x | × | 15 | − | x | x |
| = | 3880 | + | 186 | x | − | x | × | 2 | x | − | x | x |
| 3880 | + | 186 | x | − | x | × | 2 | x | − | x | x | = | 4240 |