( | X | − | 60 | ) | ( | 20 | + | 500 | − | 5 | X | ) | = | 2400 |
方程左边 = | X | ( | 20 | + | 500 | − | 5 | X | ) | − | 60 | ( | 20 | + | 500 | − | 5 | X | ) |
= | X | × | 20 | + | X | × | 500 | − | X | × | 5 | X | − | 60 | ( | 20 | + | 500 | − | 5 | X | ) |
= | 520 | X | − | X | × | 5 | X | − | 60 | ( | 20 | + | 500 | − | 5 | X | ) |
= | 520 | X | − | X | × | 5 | X | − | 60 | × | 20 | − | 60 | × | 500 | + | 60 | × | 5 | X |
= | 520 | X | − | X | × | 5 | X | − | 1200 | − | 30000 | + | 300 | X |
= | 820 | X | − | X | × | 5 | X | − | 31200 |
820 | X | − | X | × | 5 | X | − | 31200 | = | 2400 |