| ( | 750 | − | x | ) | ( | 1000 | + | x | ) | = | 75000 |
| Left side of the equation = | 750 | ( | 1000 | + | x | ) | − | x | ( | 1000 | + | x | ) |
| = | 750 | × | 1000 | + | 750 | x | − | x | ( | 1000 | + | x | ) |
| = | 750000 | + | 750 | x | − | x | ( | 1000 | + | x | ) |
| = | 750000 | + | 750 | x | − | x | × | 1000 | − | x | x |
| = | 750000 | − | 250 | x | − | x | x |
| 750000 | − | 250 | x | − | x | x | = | 75000 |