( | x | − | 30 | ) | ( | 600 | − | 10 | x | ) | = | 10000 |
方程左边 = | x | ( | 600 | − | 10 | x | ) | − | 30 | ( | 600 | − | 10 | x | ) |
= | x | × | 600 | − | x | × | 10 | x | − | 30 | ( | 600 | − | 10 | x | ) |
= | 600 | x | − | x | × | 10 | x | − | 30 | × | 600 | + | 30 | × | 10 | x |
= | 600 | x | − | x | × | 10 | x | − | 18000 | + | 300 | x |
= | 900 | x | − | x | × | 10 | x | − | 18000 |
900 | x | − | x | × | 10 | x | − | 18000 | = | 10000 |