| ( | 30 | − | 2 | x | ) | ( | 50 | − | x | ) | = | 850 |
| Left side of the equation = | 30 | ( | 50 | − | x | ) | − | 2 | x | ( | 50 | − | x | ) |
| = | 30 | × | 50 | − | 30 | x | − | 2 | x | ( | 50 | − | x | ) |
| = | 1500 | − | 30 | x | − | 2 | x | ( | 50 | − | x | ) |
| = | 1500 | − | 30 | x | − | 2 | x | × | 50 | + | 2 | x | x |
| = | 1500 | − | 30 | x | − | 100 | x | + | 2 | x | x |
| = | 1500 | − | 130 | x | + | 2 | x | x |
| 1500 | − | 130 | x | + | 2 | x | x | = | 850 |