| ( | x | − | 20 | ) | ( | 50 | − | x | − | 180 | ÷ | 10 | ) | = | 0 |
| Left side of the equation = | x | ( | 50 | − | x | − | 180 | ÷ | 10 | ) | − | 20 | ( | 50 | − | x | − | 180 | ÷ | 10 | ) |
| = | x | × | 50 | − | x | x | − | x | × | 180 | ÷ | 10 | − | 20 | ( | 50 | − | x | − | 180 | ÷ | 10 | ) |
| = | x | × | 50 | − | x | x | − | x | × | 18 | − | 20 | ( | 50 | − | x | − | 180 | ÷ | 10 | ) |
| = | 32 | x | − | x | x | − | 20 | ( | 50 | − | x | − | 180 | ÷ | 10 | ) |
| = | 32 | x | − | x | x | − | 20 | × | 50 | + | 20 | x | + | 20 | × | 180 | ÷ | 10 |
| = | 32 | x | − | x | x | − | 1000 | + | 20 | x | + | 360 |
| = | 52 | x | − | x | x | − | 640 |
| 52 | x | − | x | x | − | 640 | = | 0 |