| ( | 500 | − | 10 | x | ) | ( | 50 | + | x | − | 40 | ) | = | 800 |
| Left side of the equation = | 500 | ( | 50 | + | x | − | 40 | ) | − | 10 | x | ( | 50 | + | x | − | 40 | ) |
| = | 500 | × | 50 | + | 500 | x | − | 500 | × | 40 | − | 10 | x | ( | 50 | + | x | − | 40 | ) |
| = | 25000 | + | 500 | x | − | 20000 | − | 10 | x | ( | 50 | + | x | − | 40 | ) |
| = | 5000 | + | 500 | x | − | 10 | x | ( | 50 | + | x | − | 40 | ) |
| = | 5000 | + | 500 | x | − | 10 | x | × | 50 | − | 10 | x | x | + | 10 | x | × | 40 |
| = | 5000 | + | 500 | x | − | 500 | x | − | 10 | x | x | + | 400 | x |
| = | 5000 | + | 400 | x | − | 10 | x | x |
| 5000 | + | 400 | x | − | 10 | x | x | = | 800 |