| ( | x | − | 50 | ) | ( | - | 20 | x | + | 2600 | ) | ( | x | − | 28 | ) | = | 213 |
| Left side of the equation = | x | ( | - | 20 | x | + | 2600 | ) | ( | x | − | 28 | ) | − | 50 | ( | - | 20 | x | + | 2600 | ) | ( | x | − | 28 | ) |
| = | - | x | × | 20 | x | ( | x | − | 28 | ) | + | x | × | 2600 | ( | x | − | 28 | ) | − | 50 | ( | - | 20 | x | + | 2600 | ) | ( | x | − | 28 | ) |
| = | - | x | × | 20 | x | x | + | x | × | 20 | x | × | 28 | + | x | × | 2600 | ( | x | − | 28 | ) | − | 50 |
| = | - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | ( | x | − | 28 | ) | − | 50 | ( | - | 20 | x | + | 2600 | ) |
| = | - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | x | − | x | × | 2600 |
| = | - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | x | − | x | × | 72800 |
| = | - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | x | − | 72800 | x |
| = | - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | x | − | 72800 | x |
| = | - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | x | − | 72800 | x |
| = | - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | x | − | 72800 | x |
| = | - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | x | − | 100800 | x |
| = | - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | x | − | 100800 | x |
| = | - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | x | − | 100800 | x |
| = | - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | x | − | 230800 | x |
| - | x | × | 20 | x | x | + | x | × | 560 | x | + | x | × | 2600 | x | − | 230800 | x | = | 213 |