( | 60 | − | x | ) | ( | 200 | + | 20 | x | ) | = | 22500 | − | 2000 |
方程左边 = | 60 | ( | 200 | + | 20 | x | ) | − | x | ( | 200 | + | 20 | x | ) |
= | 60 | × | 200 | + | 60 | × | 20 | x | − | x | ( | 200 | + | 20 | x | ) |
= | 12000 | + | 1200 | x | − | x | ( | 200 | + | 20 | x | ) |
= | 12000 | + | 1200 | x | − | x | × | 200 | − | x | × | 20 | x |
= | 12000 | + | 1000 | x | − | x | × | 20 | x |
12000 | + | 1000 | x | − | x | × | 20 | x | = | 22500 | − | 2000 |
方程右边 = | 20500 |
12000 | + | 1000 | x | − | x | × | 20 | x | = | 20500 |