| ( | x | − | 40 | ) | ( | 740 | − | 10 | x | ) | = | 2640 |
| Left side of the equation = | x | ( | 740 | − | 10 | x | ) | − | 40 | ( | 740 | − | 10 | x | ) |
| = | x | × | 740 | − | x | × | 10 | x | − | 40 | ( | 740 | − | 10 | x | ) |
| = | 740 | x | − | x | × | 10 | x | − | 40 | × | 740 | + | 40 | × | 10 | x |
| = | 740 | x | − | x | × | 10 | x | − | 29600 | + | 400 | x |
| = | 1140 | x | − | x | × | 10 | x | − | 29600 |
| 1140 | x | − | x | × | 10 | x | − | 29600 | = | 2640 |