( | 800 | − | y | ) | ( | 1200 | + | 5 | y | ) | = | 854000 |
方程左边 = | 800 | ( | 1200 | + | 5 | y | ) | − | y | ( | 1200 | + | 5 | y | ) |
= | 800 | × | 1200 | + | 800 | × | 5 | y | − | y | ( | 1200 | + | 5 | y | ) |
= | 960000 | + | 4000 | y | − | y | ( | 1200 | + | 5 | y | ) |
= | 960000 | + | 4000 | y | − | y | × | 1200 | − | y | × | 5 | y |
= | 960000 | + | 2800 | y | − | y | × | 5 | y |
960000 | + | 2800 | y | − | y | × | 5 | y | = | 854000 |