400 | ( | x | + | 1 | ) | ( | x | + | 5 | ) | = | 4250 |
方程左边 = | 400 | x | ( | x | + | 5 | ) | + | 400 | × | 1 | ( | x | + | 5 | ) |
= | 400 | x | ( | x | + | 5 | ) | + | 400 | ( | x | + | 5 | ) |
= | 400 | x | x | + | 400 | x | × | 5 | + | 400 | ( | x | + | 5 | ) |
= | 400 | x | x | + | 2000 | x | + | 400 | ( | x | + | 5 | ) |
= | 400 | x | x | + | 2000 | x | + | 400 | x | + | 400 | × | 5 |
= | 400 | x | x | + | 2000 | x | + | 400 | x | + | 2000 |
= | 400 | x | x | + | 2400 | x | + | 2000 |
400 | x | x | + | 2400 | x | + | 2000 | = | 4250 |