| ( | x | − | 2 | ) | ( | 80 | − | 10 | x | ) | = | 80 |
| Left side of the equation = | x | ( | 80 | − | 10 | x | ) | − | 2 | ( | 80 | − | 10 | x | ) |
| = | x | × | 80 | − | x | × | 10 | x | − | 2 | ( | 80 | − | 10 | x | ) |
| = | 80 | x | − | x | × | 10 | x | − | 2 | × | 80 | + | 2 | × | 10 | x |
| = | 80 | x | − | x | × | 10 | x | − | 160 | + | 20 | x |
| = | 100 | x | − | x | × | 10 | x | − | 160 |
| 100 | x | − | x | × | 10 | x | − | 160 | = | 80 |