| ( | 90 | − | x | ) | ( | 100 | − | 2 | x | ) | = | 8448 |
| Left side of the equation = | 90 | ( | 100 | − | 2 | x | ) | − | x | ( | 100 | − | 2 | x | ) |
| = | 90 | × | 100 | − | 90 | × | 2 | x | − | x | ( | 100 | − | 2 | x | ) |
| = | 9000 | − | 180 | x | − | x | ( | 100 | − | 2 | x | ) |
| = | 9000 | − | 180 | x | − | x | × | 100 | + | x | × | 2 | x |
| = | 9000 | − | 280 | x | + | x | × | 2 | x |
| 9000 | − | 280 | x | + | x | × | 2 | x | = | 8448 |