6000 | = | ( | x | − | 4 | ) | ( | - | 1000 | x | + | 9000 | ) |
方程右边 = | x | ( | - | 1000 | x | + | 9000 | ) | − | 4 | ( | - | 1000 | x | + | 9000 | ) |
= | - | x | × | 1000 | x | + | x | × | 9000 | − | 4 | ( | - | 1000 | x | + | 9000 | ) |
= | - | x | × | 1000 | x | + | 9000 | x | + | 4 | × | 1000 | x | − | 4 | × | 9000 |
= | - | x | × | 1000 | x | + | 9000 | x | + | 4000 | x | − | 36000 |
= | - | x | × | 1000 | x | + | 13000 | x | − | 36000 |
6000 | = | - | x | × | 1000 | x | + | 13000 | x | − | 36000 |