| ( | 12 | − | 2 | x | ) | ( | 6 | − | 2 | x | ) | = | 40 |
| Left side of the equation = | 12 | ( | 6 | − | 2 | x | ) | − | 2 | x | ( | 6 | − | 2 | x | ) |
| = | 12 | × | 6 | − | 12 | × | 2 | x | − | 2 | x | ( | 6 | − | 2 | x | ) |
| = | 72 | − | 24 | x | − | 2 | x | ( | 6 | − | 2 | x | ) |
| = | 72 | − | 24 | x | − | 2 | x | × | 6 | + | 2 | x | × | 2 | x |
| = | 72 | − | 24 | x | − | 12 | x | + | 4 | x | x |
| = | 72 | − | 36 | x | + | 4 | x | x |
| 72 | − | 36 | x | + | 4 | x | x | = | 40 |