( | 600 | − | 10 | x | ) | ( | 40 | + | x | + | 30 | ) | = | 0 |
方程左边 = | 600 | ( | 40 | + | x | + | 30 | ) | − | 10 | x | ( | 40 | + | x | + | 30 | ) |
= | 600 | × | 40 | + | 600 | x | + | 600 | × | 30 | − | 10 | x | ( | 40 | + | x | + | 30 | ) |
= | 24000 | + | 600 | x | + | 18000 | − | 10 | x | ( | 40 | + | x | + | 30 | ) |
= | 42000 | + | 600 | x | − | 10 | x | ( | 40 | + | x | + | 30 | ) |
= | 42000 | + | 600 | x | − | 10 | x | × | 40 | − | 10 | x | x | − | 10 | x | × | 30 |
= | 42000 | + | 600 | x | − | 400 | x | − | 10 | x | x | − | 300 | x |
= | 42000 | − | 100 | x | − | 10 | x | x |
42000 | − | 100 | x | − | 10 | x | x | = | 0 |