( | 51 | − | 120 | x | ) | ( | 21 | − | 100 | x | ) | − | 441 | = | 0 |
方程左边 = | 51 | ( | 21 | − | 100 | x | ) | − | 120 | x | ( | 21 | − | 100 | x | ) | − | 441 |
= | 51 | × | 21 | − | 51 | × | 100 | x | − | 120 | x | ( | 21 | − | 100 | x | ) | − | 441 |
= | 1071 | − | 5100 | x | − | 120 | x | ( | 21 | − | 100 | x | ) | − | 441 |
= | 630 | − | 5100 | x | − | 120 | x | ( | 21 | − | 100 | x | ) |
= | 630 | − | 5100 | x | − | 120 | x | × | 21 | + | 120 | x | × | 100 | x |
= | 630 | − | 5100 | x | − | 2520 | x | + | 12000 | x | x |
= | 630 | − | 7620 | x | + | 12000 | x | x |
630 | − | 7620 | x | + | 12000 | x | x | = | 0 |