| ( | - | 9 | − | x | ) | ( | - | 1 | − | x | ) | + | 16 | = | 0 |
| Left side of the equation = | - | 9 | ( | - | 1 | − | x | ) | − | x | ( | - | 1 | − | x | ) | + | 16 |
| = | 9 | × | 1 | + | 9 | x | − | x | ( | - | 1 | − | x | ) | + | 16 |
| = | 9 | + | 9 | x | − | x | ( | - | 1 | − | x | ) | + | 16 |
| = | 25 | + | 9 | x | − | x | ( | - | 1 | − | x | ) |
| = | 25 | + | 9 | x | + | x | × | 1 | + | x | x |
| = | 25 | + | 10 | x | + | x | x |
| 25 | + | 10 | x | + | x | x | = | 0 |