( | 20 | − | 2 | x | ) | ( | 12 | − | 2 | x | ) | = | 84 |
方程左边 = | 20 | ( | 12 | − | 2 | x | ) | − | 2 | x | ( | 12 | − | 2 | x | ) |
= | 20 | × | 12 | − | 20 | × | 2 | x | − | 2 | x | ( | 12 | − | 2 | x | ) |
= | 240 | − | 40 | x | − | 2 | x | ( | 12 | − | 2 | x | ) |
= | 240 | − | 40 | x | − | 2 | x | × | 12 | + | 2 | x | × | 2 | x |
= | 240 | − | 40 | x | − | 24 | x | + | 4 | x | x |
= | 240 | − | 64 | x | + | 4 | x | x |
240 | − | 64 | x | + | 4 | x | x | = | 84 |