( | 600 | − | 20 | x | ) | ( | 1 | + | x | ) | = | 3900 |
Left side of the equation = | 600 | ( | 1 | + | x | ) | − | 20 | x | ( | 1 | + | x | ) |
= | 600 | × | 1 | + | 600 | x | − | 20 | x | ( | 1 | + | x | ) |
= | 600 | + | 600 | x | − | 20 | x | ( | 1 | + | x | ) |
= | 600 | + | 600 | x | − | 20 | x | × | 1 | − | 20 | x | x |
= | 600 | + | 600 | x | − | 20 | x | − | 20 | x | x |
= | 600 | + | 580 | x | − | 20 | x | x |
600 | + | 580 | x | − | 20 | x | x | = | 3900 |