| - | 2 | ( | x | + | 160 | ) | ( | x | − | 30 | ) | = | 800 |
| Left side of the equation = | - | 2 | x | ( | x | − | 30 | ) | − | 2 | × | 160 | ( | x | − | 30 | ) |
| = | - | 2 | x | ( | x | − | 30 | ) | − | 320 | ( | x | − | 30 | ) |
| = | - | 2 | x | x | + | 2 | x | × | 30 | − | 320 | ( | x | − | 30 | ) |
| = | - | 2 | x | x | + | 60 | x | − | 320 | ( | x | − | 30 | ) |
| = | - | 2 | x | x | + | 60 | x | − | 320 | x | + | 320 | × | 30 |
| = | - | 2 | x | x | + | 60 | x | − | 320 | x | + | 9600 |
| = | - | 2 | x | x | − | 260 | x | + | 9600 |
| - | 2 | x | x | − | 260 | x | + | 9600 | = | 800 |