| ( | x | − | 50 | ) | ( | 200 | − | 2 | x | ) | = | 800 |
| Left side of the equation = | x | ( | 200 | − | 2 | x | ) | − | 50 | ( | 200 | − | 2 | x | ) |
| = | x | × | 200 | − | x | × | 2 | x | − | 50 | ( | 200 | − | 2 | x | ) |
| = | 200 | x | − | x | × | 2 | x | − | 50 | × | 200 | + | 50 | × | 2 | x |
| = | 200 | x | − | x | × | 2 | x | − | 10000 | + | 100 | x |
| = | 300 | x | − | x | × | 2 | x | − | 10000 |
| 300 | x | − | x | × | 2 | x | − | 10000 | = | 800 |