| ( | 3969 | − | 63 | x | ) | ( | 63 | − | x | ) | = | 28 | × | 63 |
| Left side of the equation = | 3969 | ( | 63 | − | x | ) | − | 63 | x | ( | 63 | − | x | ) |
| = | 3969 | × | 63 | − | 3969 | x | − | 63 | x | ( | 63 | − | x | ) |
| = | 250047 | − | 3969 | x | − | 63 | x | ( | 63 | − | x | ) |
| = | 250047 | − | 3969 | x | − | 63 | x | × | 63 | + | 63 | x | x |
| = | 250047 | − | 3969 | x | − | 3969 | x | + | 63 | x | x |
| = | 250047 | − | 7938 | x | + | 63 | x | x |
| 250047 | − | 7938 | x | + | 63 | x | x | = | 28 | × | 63 |
| Right side of the equation = | 1764 |
| 250047 | − | 7938 | x | + | 63 | x | x | = | 1764 |