| ( | 4 | − | 2 | x | ) | ( | 30 | − | 2 | x | ) | = | 600 |
| Left side of the equation = | 4 | ( | 30 | − | 2 | x | ) | − | 2 | x | ( | 30 | − | 2 | x | ) |
| = | 4 | × | 30 | − | 4 | × | 2 | x | − | 2 | x | ( | 30 | − | 2 | x | ) |
| = | 120 | − | 8 | x | − | 2 | x | ( | 30 | − | 2 | x | ) |
| = | 120 | − | 8 | x | − | 2 | x | × | 30 | + | 2 | x | × | 2 | x |
| = | 120 | − | 8 | x | − | 60 | x | + | 4 | x | x |
| = | 120 | − | 68 | x | + | 4 | x | x |
| 120 | − | 68 | x | + | 4 | x | x | = | 600 |