| 56000 | ( | 1 | − | x | ) | ( | 1 | − | 5 | x | ÷ | 7 | ) | + | 19200 | ( | 1 | + | 5 | x | ÷ | 2 | ) | × | 7 5 | = | 78720 |
| Left side of the equation = | 56000 | ( | 1 | − | x | ) | ( | 1 | − | 5 | x | ÷ | 7 | ) | + | 26880 | ( | 1 | + | 5 | x | ÷ | 2 | ) |
| 56000 | ( | 1 | − | x | ) | ( | 1 | − | 5 | x | ÷ | 7 | ) | + | 26880 | ( | 1 | + | 5 | x | ÷ | 2 | ) | = | 78720 |
| Left side of the equation = | 56000 | × | 1 | ( | 1 | − | 5 | x | ÷ | 7 | ) | − | 56000 | x | ( | 1 | − | 5 | x | ÷ | 7 | ) | + | 26880 | ( | 1 | + | 5 | x | ÷ | 2 | ) |
| = | 56000 | ( | 1 | − | 5 | x | ÷ | 7 | ) | − | 56000 | x | ( | 1 | − | 5 | x | ÷ | 7 | ) | + | 26880 | ( | 1 | + | 5 | x | ÷ | 2 | ) |
| = | 56000 | × | 1 | − | 56000 | × | 5 | x | ÷ | 7 | − | 56000 | x | ( | 1 | − | 5 | x | ÷ | 7 | ) | + | 26880 | ( | 1 | + | 5 | x | ÷ | 2 | ) |
| = | 56000 | − | 40000 | x | − | 56000 | x | ( | 1 | − | 5 | x | ÷ | 7 | ) | + | 26880 | ( | 1 | + | 5 | x | ÷ | 2 | ) |
| = | 56000 | − | 40000 | x | − | 56000 | x | × | 1 | + | 56000 | x | × | 5 | x | ÷ | 7 | + | 26880 |
| = | 56000 | − | 40000 | x | − | 56000 | x | + | 40000 | x | x | + | 26880 | ( | 1 | + | 5 | x | ÷ | 2 | ) |
| = | 56000 | − | 96000 | x | + | 40000 | x | x | + | 26880 | ( | 1 | + | 5 | x | ÷ | 2 | ) |
| = | 56000 | − | 96000 | x | + | 40000 | x | x | + | 26880 | × | 1 | + | 26880 | × | 5 | x | ÷ | 2 |
| = | 56000 | − | 96000 | x | + | 40000 | x | x | + | 26880 | + | 67200 | x |
| = | 82880 | − | 28800 | x | + | 40000 | x | x |
| 82880 | − | 28800 | x | + | 40000 | x | x | = | 78720 |
| x1= | 1 5 |
| x2= | 13 25 |