| 2 | ( | x | + | 3 | ) | ( | x | − | 7 | ) | − | 4 | = | 56 |
| Left side of the equation = | 2 | x | ( | x | − | 7 | ) | + | 2 | × | 3 | ( | x | − | 7 | ) | − | 4 |
| = | 2 | x | ( | x | − | 7 | ) | + | 6 | ( | x | − | 7 | ) | − | 4 |
| = | 2 | x | x | − | 2 | x | × | 7 | + | 6 | ( | x | − | 7 | ) | − | 4 |
| = | 2 | x | x | − | 14 | x | + | 6 | ( | x | − | 7 | ) | − | 4 |
| = | 2 | x | x | − | 14 | x | + | 6 | x | − | 6 | × | 7 | − | 4 |
| = | 2 | x | x | − | 14 | x | + | 6 | x | − | 42 | − | 4 |
| = | 2 | x | x | − | 8 | x | − | 46 |
| 2 | x | x | − | 8 | x | − | 46 | = | 56 |