( | x | − | 30 | ) | ( | 280 | − | 10 | ( | x | − | 40 | ) | ) | = | 3450 |
方程左边 = | x | ( | 280 | − | 10 | ( | x | − | 40 | ) | ) | − | 30 | ( | 280 | − | 10 | ( | x | − | 40 | ) | ) |
= | x | × | 280 | − | x | × | 10 | ( | x | − | 40 | ) | − | 30 | ( | 280 | − | 10 | ( | x | − | 40 | ) | ) |
= | 280 | x | − | x | × | 10 | x | + | x | × | 10 | × | 40 | − | 30 | ( | 280 | − | 10 | ( | x | − | 40 | ) | ) |
= | 280 | x | − | x | × | 10 | x | + | x | × | 400 | − | 30 | ( | 280 | − | 10 | ( | x | − | 40 | ) | ) |
= | 680 | x | − | x | × | 10 | x | − | 30 | ( | 280 | − | 10 | ( | x | − | 40 | ) | ) |
= | 680 | x | − | x | × | 10 | x | − | 30 | × | 280 | + | 30 | × | 10 | ( | x | − | 40 | ) |
= | 680 | x | − | x | × | 10 | x | − | 8400 | + | 300 | ( | x | − | 40 | ) |
= | 680 | x | − | x | × | 10 | x | − | 8400 | + | 300 | x | − | 300 | × | 40 |
= | 680 | x | − | x | × | 10 | x | − | 8400 | + | 300 | x | − | 12000 |
= | 980 | x | − | x | × | 10 | x | − | 20400 |
980 | x | − | x | × | 10 | x | − | 20400 | = | 3450 |