( | X | − | 40 | ) | ( | 300 | + | 20 | ( | 60 | − | X | ) | ) | = | 6080 |
方程左边 = | X | ( | 300 | + | 20 | ( | 60 | − | X | ) | ) | − | 40 | ( | 300 | + | 20 | ( | 60 | − | X | ) | ) |
= | X | × | 300 | + | X | × | 20 | ( | 60 | − | X | ) | − | 40 | ( | 300 | + | 20 | ( | 60 | − | X | ) | ) |
= | 300 | X | + | X | × | 20 | × | 60 | − | X | × | 20 | X | − | 40 | ( | 300 | + | 20 | ( | 60 | − | X | ) | ) |
= | 300 | X | + | X | × | 1200 | − | X | × | 20 | X | − | 40 | ( | 300 | + | 20 | ( | 60 | − | X | ) | ) |
= | 1500 | X | − | X | × | 20 | X | − | 40 | ( | 300 | + | 20 | ( | 60 | − | X | ) | ) |
= | 1500 | X | − | X | × | 20 | X | − | 40 | × | 300 | − | 40 | × | 20 | ( | 60 | − | X | ) |
= | 1500 | X | − | X | × | 20 | X | − | 12000 | − | 800 | ( | 60 | − | X | ) |
= | 1500 | X | − | X | × | 20 | X | − | 12000 | − | 800 | × | 60 | + | 800 | X |
= | 1500 | X | − | X | × | 20 | X | − | 12000 | − | 48000 | + | 800 | X |
= | 2300 | X | − | X | × | 20 | X | − | 60000 |
2300 | X | − | X | × | 20 | X | − | 60000 | = | 6080 |