| ( | 25 | − | x | ) | ( | 1900 | + | 100 | x | ) | = | 0 |
| Left side of the equation = | 25 | ( | 1900 | + | 100 | x | ) | − | x | ( | 1900 | + | 100 | x | ) |
| = | 25 | × | 1900 | + | 25 | × | 100 | x | − | x | ( | 1900 | + | 100 | x | ) |
| = | 47500 | + | 2500 | x | − | x | ( | 1900 | + | 100 | x | ) |
| = | 47500 | + | 2500 | x | − | x | × | 1900 | − | x | × | 100 | x |
| = | 47500 | + | 600 | x | − | x | × | 100 | x |
| 47500 | + | 600 | x | − | x | × | 100 | x | = | 0 |