( | 40 | + | x | − | 30 | ) | ( | 200 | − | 20 | x | ) | = | 10000 |
方程左边 = | 40 | ( | 200 | − | 20 | x | ) | + | x | ( | 200 | − | 20 | x | ) | − | 30 | ( | 200 | − | 20 | x | ) |
= | 40 | × | 200 | − | 40 | × | 20 | x | + | x | ( | 200 | − | 20 | x | ) | − | 30 | ( | 200 | − | 20 | x | ) |
= | 8000 | − | 800 | x | + | x | ( | 200 | − | 20 | x | ) | − | 30 | ( | 200 | − | 20 | x | ) |
= | 8000 | − | 800 | x | + | x | × | 200 | − | x | × | 20 | x | − | 30 | ( | 200 | − | 20 | x | ) |
= | 8000 | − | 600 | x | − | x | × | 20 | x | − | 30 | ( | 200 | − | 20 | x | ) |
= | 8000 | − | 600 | x | − | x | × | 20 | x | − | 30 | × | 200 | + | 30 | × | 20 | x |
= | 8000 | − | 600 | x | − | x | × | 20 | x | − | 6000 | + | 600 | x |
= | 2000 | − | 0 | x | − | x | × | 20 | x |
2000 | − | x | × | 20 | x | = | 10000 |