| ( | 20 | − | 5 | a | ) | ( | 44 | − | a | ) | = | 1600 |
| Left side of the equation = | 20 | ( | 44 | − | a | ) | − | 5 | a | ( | 44 | − | a | ) |
| = | 20 | × | 44 | − | 20 | a | − | 5 | a | ( | 44 | − | a | ) |
| = | 880 | − | 20 | a | − | 5 | a | ( | 44 | − | a | ) |
| = | 880 | − | 20 | a | − | 5 | a | × | 44 | + | 5 | a | a |
| = | 880 | − | 20 | a | − | 220 | a | + | 5 | a | a |
| = | 880 | − | 240 | a | + | 5 | a | a |
| 880 | − | 240 | a | + | 5 | a | a | = | 1600 |