( | x | − | 20 | ) | ( | 400 | − | 20 | ( | x | − | 30 | ) | ) | = | 4320 |
方程左边 = | x | ( | 400 | − | 20 | ( | x | − | 30 | ) | ) | − | 20 | ( | 400 | − | 20 | ( | x | − | 30 | ) | ) |
= | x | × | 400 | − | x | × | 20 | ( | x | − | 30 | ) | − | 20 | ( | 400 | − | 20 | ( | x | − | 30 | ) | ) |
= | 400 | x | − | x | × | 20 | x | + | x | × | 20 | × | 30 | − | 20 | ( | 400 | − | 20 | ( | x | − | 30 | ) | ) |
= | 400 | x | − | x | × | 20 | x | + | x | × | 600 | − | 20 | ( | 400 | − | 20 | ( | x | − | 30 | ) | ) |
= | 1000 | x | − | x | × | 20 | x | − | 20 | ( | 400 | − | 20 | ( | x | − | 30 | ) | ) |
= | 1000 | x | − | x | × | 20 | x | − | 20 | × | 400 | + | 20 | × | 20 | ( | x | − | 30 | ) |
= | 1000 | x | − | x | × | 20 | x | − | 8000 | + | 400 | ( | x | − | 30 | ) |
= | 1000 | x | − | x | × | 20 | x | − | 8000 | + | 400 | x | − | 400 | × | 30 |
= | 1000 | x | − | x | × | 20 | x | − | 8000 | + | 400 | x | − | 12000 |
= | 1400 | x | − | x | × | 20 | x | − | 20000 |
1400 | x | − | x | × | 20 | x | − | 20000 | = | 4320 |