( | x | − | 60 | ) | ( | - | 20 | x | + | 2400 | ) | = | 16000 |
方程左边 = | x | ( | - | 20 | x | + | 2400 | ) | − | 60 | ( | - | 20 | x | + | 2400 | ) |
= | - | x | × | 20 | x | + | x | × | 2400 | − | 60 | ( | - | 20 | x | + | 2400 | ) |
= | - | x | × | 20 | x | + | 2400 | x | + | 60 | × | 20 | x | − | 60 | × | 2400 |
= | - | x | × | 20 | x | + | 2400 | x | + | 1200 | x | − | 144000 |
= | - | x | × | 20 | x | + | 3600 | x | − | 144000 |
- | x | × | 20 | x | + | 3600 | x | − | 144000 | = | 16000 |