( | 160 | + | 2 | x | ) | ( | 120 | − | x | ) | = | 20000 |
方程左边 = | 160 | ( | 120 | − | x | ) | + | 2 | x | ( | 120 | − | x | ) |
= | 160 | × | 120 | − | 160 | x | + | 2 | x | ( | 120 | − | x | ) |
= | 19200 | − | 160 | x | + | 2 | x | ( | 120 | − | x | ) |
= | 19200 | − | 160 | x | + | 2 | x | × | 120 | − | 2 | x | x |
= | 19200 | − | 160 | x | + | 240 | x | − | 2 | x | x |
= | 19200 | + | 80 | x | − | 2 | x | x |
19200 | + | 80 | x | − | 2 | x | x | = | 20000 |