| ( | 1 | + | 1 10 | x | ) | ( | 500 | − | 10 | x | ) | = | 800 |
| Left side of the equation = | 1 | ( | 500 | − | 10 | x | ) | + | 1 10 | x | ( | 500 | − | 10 | x | ) |
| = | 1 | × | 500 | − | 1 | × | 10 | x | + | 1 10 | x | ( | 500 | − | 10 | x | ) |
| = | 500 | − | 10 | x | + | 1 10 | x | ( | 500 | − | 10 | x | ) |
| = | 500 | − | 10 | x | + | 1 10 | x | × | 500 | − | 1 10 | x | × | 10 | x |
| = | 500 | − | 10 | x | + | 50 | x | − | 1 | x | x |
| = | 500 | + | 40 | x | − | 1 | x | x |
| 500 | + | 40 | x | − | 1 | x | x | = | 800 |