0 | = | ( | 1200 | − | 100 | x | ) | ( | 20 | + | 2 | x | ) |
方程右边 = | 1200 | ( | 20 | + | 2 | x | ) | − | 100 | x | ( | 20 | + | 2 | x | ) |
= | 1200 | × | 20 | + | 1200 | × | 2 | x | − | 100 | x | ( | 20 | + | 2 | x | ) |
= | 24000 | + | 2400 | x | − | 100 | x | ( | 20 | + | 2 | x | ) |
= | 24000 | + | 2400 | x | − | 100 | x | × | 20 | − | 100 | x | × | 2 | x |
= | 24000 | + | 2400 | x | − | 2000 | x | − | 200 | x | x |
= | 24000 | + | 400 | x | − | 200 | x | x |
0 | = | 24000 | + | 400 | x | − | 200 | x | x |