| ( | k | − | 3 | ) | ( | k | + | 1 | ) | − | ( | k | + | 6 | ) | ( | k | + | 1 | ) | = | ( | k | − | 6 | ) | ( | k | − | 3 | ) | − | ( | k | − | 3 | ) | ( | k | + | 1 | ) |
| Left side of the equation = | k | ( | k | + | 1 | ) | − | 3 | ( | k | + | 1 | ) | − | ( | k | + | 6 | ) | ( | k | + | 1 | ) |
| = | k | k | + | k | × | 1 | − | 3 | ( | k | + | 1 | ) | − | ( | k | + | 6 | ) | ( | k | + | 1 | ) |
| = | k | k | + | 1 | k | − | 3 | k | − | 3 | × | 1 | − | ( | k | + | 6 | ) | ( | k | + | 1 | ) |
| = | k | k | + | 1 | k | − | 3 | k | − | 3 | − | ( | k | + | 6 | ) | ( | k | + | 1 | ) |
| = | k | k | − | 2 | k | − | 3 | − | ( | k | + | 6 | ) | ( | k | + | 1 | ) |
| = | k | k | − | 2 | k | − | 3 | − | k | ( | k | + | 1 | ) | − | 6 | ( | k | + | 1 | ) |
| = | k | k | − | 2 | k | − | 3 | − | k | k | − | k | × | 1 | − | 6 | ( | k | + | 1 | ) |
| = | k | k | − | 3 | k | − | 3 | − | k | k | − | 6 | ( | k | + | 1 | ) |
| = | k | k | − | 3 | k | − | 3 | − | k | k | − | 6 | k | − | 6 | × | 1 |
| = | k | k | − | 3 | k | − | 3 | − | k | k | − | 6 | k | − | 6 |
| = | k | k | − | 9 | k | − | 9 | − | k | k |
| k | k | − | 9 | k | − | 9 | − | k | k | = | ( | k | − | 6 | ) | ( | k | − | 3 | ) | − | ( | k | − | 3 | ) | ( | k | + | 1 | ) |
| Right side of the equation = | k | ( | k | − | 3 | ) | − | 6 | ( | k | − | 3 | ) | − | ( | k | − | 3 | ) | ( | k | + | 1 | ) |
| = | k | k | − | k | × | 3 | − | 6 | ( | k | − | 3 | ) | − | ( | k | − | 3 | ) | ( | k | + | 1 | ) |
| = | k | k | − | 3 | k | − | 6 | k | + | 6 | × | 3 | − | ( | k | − | 3 | ) | ( | k | + | 1 | ) |
| = | k | k | − | 3 | k | − | 6 | k | + | 18 | − | ( | k | − | 3 | ) | ( | k | + | 1 | ) |
| = | k | k | − | 9 | k | + | 18 | − | ( | k | − | 3 | ) | ( | k | + | 1 | ) |
| = | k | k | − | 9 | k | + | 18 | − | k | ( | k | + | 1 | ) | + | 3 | ( | k | + | 1 | ) |
| = | k | k | − | 9 | k | + | 18 | − | k | k | − | k | × | 1 | + | 3 | ( | k | + | 1 | ) |
| = | k | k | − | 10 | k | + | 18 | − | k | k | + | 3 | ( | k | + | 1 | ) |
| = | k | k | − | 10 | k | + | 18 | − | k | k | + | 3 | k | + | 3 | × | 1 |
| = | k | k | − | 10 | k | + | 18 | − | k | k | + | 3 | k | + | 3 |
| = | k | k | − | 7 | k | + | 21 | − | k | k |
| k | k | − | 9 | k | − | 9 | − | k | k | = | k | k | − | 7 | k | + | 21 | − | k | k |