| ( | 19 | − | 2 | x | ) | ( | 15 | − | 2 | x | ) | = | 77 |
| Left side of the equation = | 19 | ( | 15 | − | 2 | x | ) | − | 2 | x | ( | 15 | − | 2 | x | ) |
| = | 19 | × | 15 | − | 19 | × | 2 | x | − | 2 | x | ( | 15 | − | 2 | x | ) |
| = | 285 | − | 38 | x | − | 2 | x | ( | 15 | − | 2 | x | ) |
| = | 285 | − | 38 | x | − | 2 | x | × | 15 | + | 2 | x | × | 2 | x |
| = | 285 | − | 38 | x | − | 30 | x | + | 4 | x | x |
| = | 285 | − | 68 | x | + | 4 | x | x |
| 285 | − | 68 | x | + | 4 | x | x | = | 77 |