| ( | x | − | 60 | ) | ( | 20 | + | 2 | x | ) | = | 20 |
| Left side of the equation = | x | ( | 20 | + | 2 | x | ) | − | 60 | ( | 20 | + | 2 | x | ) |
| = | x | × | 20 | + | x | × | 2 | x | − | 60 | ( | 20 | + | 2 | x | ) |
| = | 20 | x | + | x | × | 2 | x | − | 60 | × | 20 | − | 60 | × | 2 | x |
| = | 20 | x | + | x | × | 2 | x | − | 1200 | − | 120 | x |
| = | - | 100 | x | + | x | × | 2 | x | − | 1200 |
| - | 100 | x | + | x | × | 2 | x | − | 1200 | = | 20 |