( | 51000000 | − | 120000 | x | ) | ( | 21000000 | − | 100000 | x | ) | − | 441000000000000 | = | 0 |
方程左边 = | 51000000 | ( | 21000000 | − | 100000 | x | ) | − | 120000 | x | ( | 21000000 | − | 100000 | x | ) | − | 441000000000000 |
= | 51000000 | × | 21000000 | − | 51000000 | × | 100000 | x | − | 120000 | x | ( | 21000000 | − | 100000 | x | ) | − | 441000000000000 |