( | 10 | + | x | − | 8 | ) | ( | 200 | − | 20 | x | ) | = | 640 |
方程左边 = | 10 | ( | 200 | − | 20 | x | ) | + | x | ( | 200 | − | 20 | x | ) | − | 8 | ( | 200 | − | 20 | x | ) |
= | 10 | × | 200 | − | 10 | × | 20 | x | + | x | ( | 200 | − | 20 | x | ) | − | 8 | ( | 200 | − | 20 | x | ) |
= | 2000 | − | 200 | x | + | x | ( | 200 | − | 20 | x | ) | − | 8 | ( | 200 | − | 20 | x | ) |
= | 2000 | − | 200 | x | + | x | × | 200 | − | x | × | 20 | x | − | 8 | ( | 200 | − | 20 | x | ) |
= | 2000 | − | 0 | x | − | x | × | 20 | x | − | 8 | ( | 200 | − | 20 | x | ) |
= | 2000 | − | x | × | 20 | x | − | 8 | × | 200 | + | 8 | × | 20 | x |
= | 2000 | − | x | × | 20 | x | − | 1600 | + | 160 | x |
= | 400 | − | x | × | 20 | x | + | 160 | x |
400 | − | x | × | 20 | x | + | 160 | x | = | 640 |