| ( | 9 | − | 2 | x | ) | ( | 5 | − | 2 | x | ) | = | 18 |
| Left side of the equation = | 9 | ( | 5 | − | 2 | x | ) | − | 2 | x | ( | 5 | − | 2 | x | ) |
| = | 9 | × | 5 | − | 9 | × | 2 | x | − | 2 | x | ( | 5 | − | 2 | x | ) |
| = | 45 | − | 18 | x | − | 2 | x | ( | 5 | − | 2 | x | ) |
| = | 45 | − | 18 | x | − | 2 | x | × | 5 | + | 2 | x | × | 2 | x |
| = | 45 | − | 18 | x | − | 10 | x | + | 4 | x | x |
| = | 45 | − | 28 | x | + | 4 | x | x |
| 45 | − | 28 | x | + | 4 | x | x | = | 18 |