( | x | − | 10 | ) | ( | - | 10 | x | + | 300 | ) | = | 840 |
Left side of the equation = | x | ( | - | 10 | x | + | 300 | ) | − | 10 | ( | - | 10 | x | + | 300 | ) |
= | - | x | × | 10 | x | + | x | × | 300 | − | 10 | ( | - | 10 | x | + | 300 | ) |
= | - | x | × | 10 | x | + | 300 | x | + | 10 | × | 10 | x | − | 10 | × | 300 |
= | - | x | × | 10 | x | + | 300 | x | + | 100 | x | − | 3000 |
= | - | x | × | 10 | x | + | 400 | x | − | 3000 |
- | x | × | 10 | x | + | 400 | x | − | 3000 | = | 840 |