| ( | 40 | − | 2 | x | ) | ( | 26 | − | x | ) | = | 864 |
| Left side of the equation = | 40 | ( | 26 | − | x | ) | − | 2 | x | ( | 26 | − | x | ) |
| = | 40 | × | 26 | − | 40 | x | − | 2 | x | ( | 26 | − | x | ) |
| = | 1040 | − | 40 | x | − | 2 | x | ( | 26 | − | x | ) |
| = | 1040 | − | 40 | x | − | 2 | x | × | 26 | + | 2 | x | x |
| = | 1040 | − | 40 | x | − | 52 | x | + | 2 | x | x |
| = | 1040 | − | 92 | x | + | 2 | x | x |
| 1040 | − | 92 | x | + | 2 | x | x | = | 864 |