( | 40 | − | 25 | − | x | ) | ( | 400 | + | 5 | x | ) | = | 4250 |
方程左边 = | 40 | ( | 400 | + | 5 | x | ) | − | 25 | ( | 400 | + | 5 | x | ) | − | x | ( | 400 | + | 5 | x | ) |
= | 40 | × | 400 | + | 40 | × | 5 | x | − | 25 | ( | 400 | + | 5 | x | ) | − | x | ( | 400 | + | 5 | x | ) |
= | 16000 | + | 200 | x | − | 25 | ( | 400 | + | 5 | x | ) | − | x | ( | 400 | + | 5 | x | ) |
= | 16000 | + | 200 | x | − | 25 | × | 400 | − | 25 | × | 5 | x | − | x | ( | 400 | + | 5 | x | ) |
= | 16000 | + | 200 | x | − | 10000 | − | 125 | x | − | x | ( | 400 | + | 5 | x | ) |
= | 6000 | + | 75 | x | − | x | ( | 400 | + | 5 | x | ) |
= | 6000 | + | 75 | x | − | x | × | 400 | − | x | × | 5 | x |
= | 6000 | − | 325 | x | − | x | × | 5 | x |
6000 | − | 325 | x | − | x | × | 5 | x | = | 4250 |