| ( | x | + | 15 | ) | ( | x | + | 20 | ) | − | x | x | = | 2050 |
| Left side of the equation = | x | ( | x | + | 20 | ) | + | 15 | ( | x | + | 20 | ) | − | x | x |
| = | x | x | + | x | × | 20 | + | 15 | ( | x | + | 20 | ) | − | x | x |
| = | x | x | + | 20 | x | + | 15 | x | + | 15 | × | 20 | − | x | x |
| = | x | x | + | 20 | x | + | 15 | x | + | 300 | − | x | x |
| = | x | x | + | 35 | x | + | 300 | − | x | x |
| x | x | + | 35 | x | + | 300 | − | x | x | = | 2050 |