| ( | x | − | 30 | ) | ( | 10 | x | − | 400 | ) | = | 10000 |
| Left side of the equation = | x | ( | 10 | x | − | 400 | ) | − | 30 | ( | 10 | x | − | 400 | ) |
| = | x | × | 10 | x | − | x | × | 400 | − | 30 | ( | 10 | x | − | 400 | ) |
| = | x | × | 10 | x | − | 400 | x | − | 30 | × | 10 | x | + | 30 | × | 400 |
| = | x | × | 10 | x | − | 400 | x | − | 300 | x | + | 12000 |
| = | x | × | 10 | x | − | 700 | x | + | 12000 |
| x | × | 10 | x | − | 700 | x | + | 12000 | = | 10000 |