| ( | X | − | 50 | ) | ( | 200 | − | 2 | X | ) | = | 1200 |
| Left side of the equation = | X | ( | 200 | − | 2 | X | ) | − | 50 | ( | 200 | − | 2 | X | ) |
| = | X | × | 200 | − | X | × | 2 | X | − | 50 | ( | 200 | − | 2 | X | ) |
| = | 200 | X | − | X | × | 2 | X | − | 50 | × | 200 | + | 50 | × | 2 | X |
| = | 200 | X | − | X | × | 2 | X | − | 10000 | + | 100 | X |
| = | 300 | X | − | X | × | 2 | X | − | 10000 |
| 300 | X | − | X | × | 2 | X | − | 10000 | = | 1200 |