( | 60 | − | x | − | 40 | ) | ( | 300 | + | 50 | x | ) | = | 0 |
方程左边 = | 60 | ( | 300 | + | 50 | x | ) | − | x | ( | 300 | + | 50 | x | ) | − | 40 | ( | 300 | + | 50 | x | ) |
= | 60 | × | 300 | + | 60 | × | 50 | x | − | x | ( | 300 | + | 50 | x | ) | − | 40 | ( | 300 | + | 50 | x | ) |
= | 18000 | + | 3000 | x | − | x | ( | 300 | + | 50 | x | ) | − | 40 | ( | 300 | + | 50 | x | ) |
= | 18000 | + | 3000 | x | − | x | × | 300 | − | x | × | 50 | x | − | 40 | ( | 300 | + | 50 | x | ) |
= | 18000 | + | 2700 | x | − | x | × | 50 | x | − | 40 | ( | 300 | + | 50 | x | ) |
= | 18000 | + | 2700 | x | − | x | × | 50 | x | − | 40 | × | 300 | − | 40 | × | 50 | x |
= | 18000 | + | 2700 | x | − | x | × | 50 | x | − | 12000 | − | 2000 | x |
= | 6000 | + | 700 | x | − | x | × | 50 | x |
6000 | + | 700 | x | − | x | × | 50 | x | = | 0 |