| 5 | ( | x | + | 1 | ) | ( | x | − | 1 | ) | = | 7 | x |
| Left side of the equation = | 5 | x | ( | x | − | 1 | ) | + | 5 | × | 1 | ( | x | − | 1 | ) |
| = | 5 | x | ( | x | − | 1 | ) | + | 5 | ( | x | − | 1 | ) |
| = | 5 | x | x | − | 5 | x | × | 1 | + | 5 | ( | x | − | 1 | ) |
| = | 5 | x | x | − | 5 | x | + | 5 | ( | x | − | 1 | ) |
| = | 5 | x | x | − | 5 | x | + | 5 | x | − | 5 | × | 1 |
| = | 5 | x | x | − | 5 | x | + | 5 | x | − | 5 |
| = | 5 | x | x | − | 0 | x | − | 5 |
| 5 | x | x | − | 0 | x | − | 5 | = | 7 | x |