| ( | x | + | 1 | ) | ( | 600 | − | 20 | x | ) | = | 2600 |
| Left side of the equation = | x | ( | 600 | − | 20 | x | ) | + | 1 | ( | 600 | − | 20 | x | ) |
| = | x | × | 600 | − | x | × | 20 | x | + | 1 | ( | 600 | − | 20 | x | ) |
| = | 600 | x | − | x | × | 20 | x | + | 1 | × | 600 | − | 1 | × | 20 | x |
| = | 600 | x | − | x | × | 20 | x | + | 600 | − | 20 | x |
| = | 580 | x | − | x | × | 20 | x | + | 600 |
| 580 | x | − | x | × | 20 | x | + | 600 | = | 2600 |