( | 35 | − | X | ) | ( | 600 | + | 30 | X | ) | = | 22500 |
方程左边 = | 35 | ( | 600 | + | 30 | X | ) | − | X | ( | 600 | + | 30 | X | ) |
= | 35 | × | 600 | + | 35 | × | 30 | X | − | X | ( | 600 | + | 30 | X | ) |
= | 21000 | + | 1050 | X | − | X | ( | 600 | + | 30 | X | ) |
= | 21000 | + | 1050 | X | − | X | × | 600 | − | X | × | 30 | X |
= | 21000 | + | 450 | X | − | X | × | 30 | X |
21000 | + | 450 | X | − | X | × | 30 | X | = | 22500 |