| ( | 40 | − | 2 | x | ) | ( | 25 | − | 2 | x | ) | = | 450 |
| Left side of the equation = | 40 | ( | 25 | − | 2 | x | ) | − | 2 | x | ( | 25 | − | 2 | x | ) |
| = | 40 | × | 25 | − | 40 | × | 2 | x | − | 2 | x | ( | 25 | − | 2 | x | ) |
| = | 1000 | − | 80 | x | − | 2 | x | ( | 25 | − | 2 | x | ) |
| = | 1000 | − | 80 | x | − | 2 | x | × | 25 | + | 2 | x | × | 2 | x |
| = | 1000 | − | 80 | x | − | 50 | x | + | 4 | x | x |
| = | 1000 | − | 130 | x | + | 4 | x | x |
| 1000 | − | 130 | x | + | 4 | x | x | = | 450 |
| x2= | 55 2 |