( | 20 | − | y | ) | ( | 500 | + | 50 | y | ) | = | 10800 |
方程左边 = | 20 | ( | 500 | + | 50 | y | ) | − | y | ( | 500 | + | 50 | y | ) |
= | 20 | × | 500 | + | 20 | × | 50 | y | − | y | ( | 500 | + | 50 | y | ) |
= | 10000 | + | 1000 | y | − | y | ( | 500 | + | 50 | y | ) |
= | 10000 | + | 1000 | y | − | y | × | 500 | − | y | × | 50 | y |
= | 10000 | + | 500 | y | − | y | × | 50 | y |
10000 | + | 500 | y | − | y | × | 50 | y | = | 10800 |