| ( | 2 | x | + | 8 | ) | ( | 210 | − | x | ) | = | 0 |
| Left side of the equation = | 2 | x | ( | 210 | − | x | ) | + | 8 | ( | 210 | − | x | ) |
| = | 2 | x | × | 210 | − | 2 | x | x | + | 8 | ( | 210 | − | x | ) |
| = | 420 | x | − | 2 | x | x | + | 8 | ( | 210 | − | x | ) |
| = | 420 | x | − | 2 | x | x | + | 8 | × | 210 | − | 8 | x |
| = | 420 | x | − | 2 | x | x | + | 1680 | − | 8 | x |
| = | 412 | x | − | 2 | x | x | + | 1680 |
| 412 | x | − | 2 | x | x | + | 1680 | = | 0 |