| ( | 35 | − | 2 | x | ) | ( | 20 | − | x | ) | = | 558 |
| Left side of the equation = | 35 | ( | 20 | − | x | ) | − | 2 | x | ( | 20 | − | x | ) |
| = | 35 | × | 20 | − | 35 | x | − | 2 | x | ( | 20 | − | x | ) |
| = | 700 | − | 35 | x | − | 2 | x | ( | 20 | − | x | ) |
| = | 700 | − | 35 | x | − | 2 | x | × | 20 | + | 2 | x | x |
| = | 700 | − | 35 | x | − | 40 | x | + | 2 | x | x |
| = | 700 | − | 75 | x | + | 2 | x | x |
| 700 | − | 75 | x | + | 2 | x | x | = | 558 |
| x2= | 71 2 |