| ( | 1 5 | x | + | 3 | ) | ( | 3000 | − | 10 | x | ) | = | 29000 |
| 方程左边 = | 1 5 | x | ( | 3000 | − | 10 | x | ) | + | 3 | ( | 3000 | − | 10 | x | ) |
| = | 1 5 | x | × | 3000 | − | 1 5 | x | × | 10 | x | + | 3 | ( | 3000 | − | 10 | x | ) |
| = | 600 | x | − | 2 | x | x | + | 3 | ( | 3000 | − | 10 | x | ) |
| = | 600 | x | − | 2 | x | x | + | 3 | × | 3000 | − | 3 | × | 10 | x |
| = | 600 | x | − | 2 | x | x | + | 9000 | − | 30 | x |
| = | 570 | x | − | 2 | x | x | + | 9000 |
| 570 | x | − | 2 | x | x | + | 9000 | = | 29000 |