( | x | − | 40 | ) | ( | 30 | + | 20 | ( | 60 | − | x | ) | ) | = | 6120 |
方程左边 = | x | ( | 30 | + | 20 | ( | 60 | − | x | ) | ) | − | 40 | ( | 30 | + | 20 | ( | 60 | − | x | ) | ) |
= | x | × | 30 | + | x | × | 20 | ( | 60 | − | x | ) | − | 40 | ( | 30 | + | 20 | ( | 60 | − | x | ) | ) |
= | 30 | x | + | x | × | 20 | × | 60 | − | x | × | 20 | x | − | 40 | ( | 30 | + | 20 | ( | 60 | − | x | ) | ) |
= | 30 | x | + | x | × | 1200 | − | x | × | 20 | x | − | 40 | ( | 30 | + | 20 | ( | 60 | − | x | ) | ) |
= | 1230 | x | − | x | × | 20 | x | − | 40 | ( | 30 | + | 20 | ( | 60 | − | x | ) | ) |
= | 1230 | x | − | x | × | 20 | x | − | 40 | × | 30 | − | 40 | × | 20 | ( | 60 | − | x | ) |
= | 1230 | x | − | x | × | 20 | x | − | 1200 | − | 800 | ( | 60 | − | x | ) |
= | 1230 | x | − | x | × | 20 | x | − | 1200 | − | 800 | × | 60 | + | 800 | x |
= | 1230 | x | − | x | × | 20 | x | − | 1200 | − | 48000 | + | 800 | x |
= | 2030 | x | − | x | × | 20 | x | − | 49200 |
2030 | x | − | x | × | 20 | x | − | 49200 | = | 6120 |