| 800 | = | ( | x | − | 50 | ) | ( | 2 | x | − | 20 | ) |
| Right side of the equation = | x | ( | 2 | x | − | 20 | ) | − | 50 | ( | 2 | x | − | 20 | ) |
| = | x | × | 2 | x | − | x | × | 20 | − | 50 | ( | 2 | x | − | 20 | ) |
| = | x | × | 2 | x | − | 20 | x | − | 50 | × | 2 | x | + | 50 | × | 20 |
| = | x | × | 2 | x | − | 20 | x | − | 100 | x | + | 1000 |
| = | x | × | 2 | x | − | 120 | x | + | 1000 |
| 800 | = | x | × | 2 | x | − | 120 | x | + | 1000 |