( | x | − | 30 | ) | ( | 400 | − | 10 | ( | x | − | 40 | ) | ) | = | 5250 |
方程左边 = | x | ( | 400 | − | 10 | ( | x | − | 40 | ) | ) | − | 30 | ( | 400 | − | 10 | ( | x | − | 40 | ) | ) |
= | x | × | 400 | − | x | × | 10 | ( | x | − | 40 | ) | − | 30 | ( | 400 | − | 10 | ( | x | − | 40 | ) | ) |
= | 400 | x | − | x | × | 10 | x | + | x | × | 10 | × | 40 | − | 30 | ( | 400 | − | 10 | ( | x | − | 40 | ) | ) |
= | 400 | x | − | x | × | 10 | x | + | x | × | 400 | − | 30 | ( | 400 | − | 10 | ( | x | − | 40 | ) | ) |
= | 800 | x | − | x | × | 10 | x | − | 30 | ( | 400 | − | 10 | ( | x | − | 40 | ) | ) |
= | 800 | x | − | x | × | 10 | x | − | 30 | × | 400 | + | 30 | × | 10 | ( | x | − | 40 | ) |
= | 800 | x | − | x | × | 10 | x | − | 12000 | + | 300 | ( | x | − | 40 | ) |
= | 800 | x | − | x | × | 10 | x | − | 12000 | + | 300 | x | − | 300 | × | 40 |
= | 800 | x | − | x | × | 10 | x | − | 12000 | + | 300 | x | − | 12000 |
= | 1100 | x | − | x | × | 10 | x | − | 24000 |
1100 | x | − | x | × | 10 | x | − | 24000 | = | 5250 |