| ( | 2 | − | x | ) | ( | 800 | x | + | 400 | ) | = | 1200 |
| Left side of the equation = | 2 | ( | 800 | x | + | 400 | ) | − | x | ( | 800 | x | + | 400 | ) |
| = | 2 | × | 800 | x | + | 2 | × | 400 | − | x | ( | 800 | x | + | 400 | ) |
| = | 1600 | x | + | 800 | − | x | ( | 800 | x | + | 400 | ) |
| = | 1600 | x | + | 800 | − | x | × | 800 | x | − | x | × | 400 |
| = | 1200 | x | + | 800 | − | x | × | 800 | x |
| 1200 | x | + | 800 | − | x | × | 800 | x | = | 1200 |
| x1= | 1 2 |
| x2=1 |