( | x | − | 800 | ) | x | ( | 1 | − | 20 | ) | + | 800 | = | 1760 |
方程左边 = | x | x | ( | 1 | − | 20 | ) | − | 800 | x | ( | 1 | − | 20 | ) | + | 800 |
= | x | x | × | 1 | − | x | x | × | 20 | − | 800 | x | ( | 1 | − | 20 | ) | + | 800 |
= | x | x | × | 1 | − | x | x | × | 20 | − | 800 | x | × | 1 | + | 800 | x | × | 20 |
= | x | x | × | 1 | − | x | x | × | 20 | − | 800 | x | + | 16000 | x | + | 800 |
= | x | x | × | 1 | − | x | x | × | 20 | + | 15200 | x | + | 800 |
x | x | × | 1 | − | x | x | × | 20 | + | 15200 | x | + | 800 | = | 1760 |