( | 3 10 | − | x | ) | ( | 500 | + | 100 | x | ) | = | 120 |
方程左边 = | 3 10 | ( | 500 | + | 100 | x | ) | − | x | ( | 500 | + | 100 | x | ) |
= | 3 10 | × | 500 | + | 3 10 | × | 100 | x | − | x | ( | 500 | + | 100 | x | ) |
= | 150 | + | 30 | x | − | x | ( | 500 | + | 100 | x | ) |
= | 150 | + | 30 | x | − | x | × | 500 | − | x | × | 100 | x |
= | 150 | − | 470 | x | − | x | × | 100 | x |
150 | − | 470 | x | − | x | × | 100 | x | = | 120 |