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