| ( | - | 400 | x | + | 4000 | ) | ( | 2 | x | + | 1 | ) | − | ( | - | 400 | x | + | 4000 | ) | x | = | 5600 |
| Left side of the equation = | - | 400 | x | ( | 2 | x | + | 1 | ) | + | 4000 | ( | 2 | x | + | 1 | ) | − | ( | - | 400 | x | + | 4000 | ) | x |
| = | - | 400 | x | × | 2 | x | − | 400 | x | × | 1 | + | 4000 | ( | 2 | x | + | 1 | ) | − | ( | - | 400 | x | + | 4000 | ) | x |
| = | - | 800 | x | x | − | 400 | x | + | 4000 | ( | 2 | x | + | 1 | ) | − | ( | - | 400 | x | + | 4000 | ) | x |
| = | - | 800 | x | x | − | 400 | x | + | 4000 | × | 2 | x | + | 4000 | × | 1 | − | ( | - | 400 | x | + | 4000 | ) | x |
| = | - | 800 | x | x | − | 400 | x | + | 8000 | x | + | 4000 | − | ( | - | 400 | x | + | 4000 | ) | x |
| = | - | 800 | x | x | + | 7600 | x | + | 4000 | − | ( | - | 400 | x | + | 4000 | ) | x |
| = | - | 800 | x | x | + | 7600 | x | + | 4000 | + | 400 | x | x | − | 4000 | x |
| = | - | 800 | x | x | + | 3600 | x | + | 4000 | + | 400 | x | x |
| - | 800 | x | x | + | 3600 | x | + | 4000 | + | 400 | x | x | = | 5600 |