10 | ( | 2 | x | − | 20 | ) | ( | x | − | 20 | ) | = | 1500 |
方程左边 = | 10 | × | 2 | x | ( | x | − | 20 | ) | − | 10 | × | 20 | ( | x | − | 20 | ) |
= | 20 | x | ( | x | − | 20 | ) | − | 200 | ( | x | − | 20 | ) |
= | 20 | x | x | − | 20 | x | × | 20 | − | 200 | ( | x | − | 20 | ) |
= | 20 | x | x | − | 400 | x | − | 200 | ( | x | − | 20 | ) |
= | 20 | x | x | − | 400 | x | − | 200 | x | + | 200 | × | 20 |
= | 20 | x | x | − | 400 | x | − | 200 | x | + | 4000 |
= | 20 | x | x | − | 600 | x | + | 4000 |
20 | x | x | − | 600 | x | + | 4000 | = | 1500 |