| ( | 90 | − | 2 | x | ) | ( | 40 | − | 2 | x | ) | = | 90 | × | 40 | × | 18 25 |
| Left side of the equation = | 90 | ( | 40 | − | 2 | x | ) | − | 2 | x | ( | 40 | − | 2 | x | ) |
| = | 90 | × | 40 | − | 90 | × | 2 | x | − | 2 | x | ( | 40 | − | 2 | x | ) |
| = | 3600 | − | 180 | x | − | 2 | x | ( | 40 | − | 2 | x | ) |
| = | 3600 | − | 180 | x | − | 2 | x | × | 40 | + | 2 | x | × | 2 | x |
| = | 3600 | − | 180 | x | − | 80 | x | + | 4 | x | x |
| = | 3600 | − | 260 | x | + | 4 | x | x |
| 3600 | − | 260 | x | + | 4 | x | x | = | 90 | × | 40 | × | 18 25 |
| Right side of the equation = | 2592 |
| 3600 | − | 260 | x | + | 4 | x | x | = | 2592 |