| 90 | ( | 1 | − | x | ) | ( | 1 | − | x | ) | = | 40 |
| Left side of the equation = | 90 | × | 1 | ( | 1 | − | x | ) | − | 90 | x | ( | 1 | − | x | ) |
| = | 90 | ( | 1 | − | x | ) | − | 90 | x | ( | 1 | − | x | ) |
| = | 90 | × | 1 | − | 90 | x | − | 90 | x | ( | 1 | − | x | ) |
| = | 90 | − | 90 | x | − | 90 | x | ( | 1 | − | x | ) |
| = | 90 | − | 90 | x | − | 90 | x | × | 1 | + | 90 | x | x |
| = | 90 | − | 90 | x | − | 90 | x | + | 90 | x | x |
| = | 90 | − | 180 | x | + | 90 | x | x |
| 90 | − | 180 | x | + | 90 | x | x | = | 40 |
| x1= | 1 3 |
| x2= | 5 3 |