| ( | x | − | 10 | ) | ( | - | 20 | x | + | 920 | ) | = | 3100 |
| Left side of the equation = | x | ( | - | 20 | x | + | 920 | ) | − | 10 | ( | - | 20 | x | + | 920 | ) |
| = | - | x | × | 20 | x | + | x | × | 920 | − | 10 | ( | - | 20 | x | + | 920 | ) |
| = | - | x | × | 20 | x | + | 920 | x | + | 10 | × | 20 | x | − | 10 | × | 920 |
| = | - | x | × | 20 | x | + | 920 | x | + | 200 | x | − | 9200 |
| = | - | x | × | 20 | x | + | 1120 | x | − | 9200 |
| - | x | × | 20 | x | + | 1120 | x | − | 9200 | = | 3100 |