( | 19 | − | x | ) | ( | 3000 | + | 30 | x | ) | = | 6300 |
方程左边 = | 19 | ( | 3000 | + | 30 | x | ) | − | x | ( | 3000 | + | 30 | x | ) |
= | 19 | × | 3000 | + | 19 | × | 30 | x | − | x | ( | 3000 | + | 30 | x | ) |
= | 57000 | + | 570 | x | − | x | ( | 3000 | + | 30 | x | ) |
= | 57000 | + | 570 | x | − | x | × | 3000 | − | x | × | 30 | x |
= | 57000 | − | 2430 | x | − | x | × | 30 | x |
57000 | − | 2430 | x | − | x | × | 30 | x | = | 6300 |