| ( | X | + | 3 | ) | ( | X | − | 10 | ) | = | X | × | 2 | − | 2 | X | − | 15 |
| Left side of the equation = | X | ( | X | − | 10 | ) | + | 3 | ( | X | − | 10 | ) |
| = | X | X | − | X | × | 10 | + | 3 | ( | X | − | 10 | ) |
| = | X | X | − | 10 | X | + | 3 | X | − | 3 | × | 10 |
| = | X | X | − | 10 | X | + | 3 | X | − | 30 |
| = | X | X | − | 7 | X | − | 30 |
| X | X | − | 7 | X | − | 30 | = | X | × | 2 | − | 2 | X | − | 15 |
| Right side of the equation = | 0 | X | − | 15 |
| X | X | − | 7 | X | − | 30 | = | 0 | X | − | 15 |