( | x | − | 30 | ) | ( | 600 | − | ( | x | − | 40 | ) | × | 20 | ) | = | 10000 |
方程左边 = | x | ( | 600 | − | ( | x | − | 40 | ) | × | 20 | ) | − | 30 | ( | 600 | − | ( | x | − | 40 | ) | × | 20 | ) |
= | x | × | 600 | − | x | ( | x | − | 40 | ) | × | 20 | − | 30 | ( | 600 | − | ( | x | − | 40 | ) | × | 20 | ) |
= | 600 | x | − | x | x | × | 20 | + | x | × | 40 | × | 20 | − | 30 | ( | 600 | − | ( | x | − | 40 | ) | × | 20 | ) |
= | 600 | x | − | x | x | × | 20 | + | x | × | 800 | − | 30 | ( | 600 | − | ( | x | − | 40 | ) | × | 20 | ) |
= | 1400 | x | − | x | x | × | 20 | − | 30 | ( | 600 | − | ( | x | − | 40 | ) | × | 20 | ) |
= | 1400 | x | − | x | x | × | 20 | − | 30 | × | 600 | + | 30 | ( | x | − | 40 | ) | × | 20 |
= | 1400 | x | − | x | x | × | 20 | − | 18000 | + | 600 | ( | x | − | 40 | ) |
= | 1400 | x | − | x | x | × | 20 | − | 18000 | + | 600 | x | − | 600 | × | 40 |
= | 1400 | x | − | x | x | × | 20 | − | 18000 | + | 600 | x | − | 24000 |
= | 2000 | x | − | x | x | × | 20 | − | 42000 |
2000 | x | − | x | x | × | 20 | − | 42000 | = | 10000 |