( | 300 | − | 10 | a | ) | ( | 40 | − | a | ) | − | ( | 800 | − | 15 | a | ) | = | 11350 |
方程左边 = | 300 | ( | 40 | − | a | ) | − | 10 | a | ( | 40 | − | a | ) | − | ( | 800 | − | 15 | a | ) |
= | 300 | × | 40 | − | 300 | a | − | 10 | a | ( | 40 | − | a | ) | − | ( | 800 | − | 15 | a | ) |
= | 12000 | − | 300 | a | − | 10 | a | ( | 40 | − | a | ) | − | ( | 800 | − | 15 | a | ) |
= | 12000 | − | 300 | a | − | 10 | a | × | 40 | + | 10 | a | a | − | ( | 800 | − | 15 | a | ) |
= | 12000 | − | 300 | a | − | 400 | a | + | 10 | a | a | − | ( | 800 | − | 15 | a | ) |
= | 12000 | − | 700 | a | + | 10 | a | a | − | ( | 800 | − | 15 | a | ) |
= | 12000 | − | 700 | a | + | 10 | a | a | − | 800 | + | 15 | a |
= | 11200 | − | 685 | a | + | 10 | a | a |
11200 | − | 685 | a | + | 10 | a | a | = | 11350 |