( | C | × | 21 | ) | × | 2 5 | ( | 1 | − | 2 5 | ) | × | 1 5 | = | 0 |
方程左边 = | ( | C | × | 21 | ) | × | 2 25 | ( | 1 | − | 2 5 | ) |
( | C | × | 21 | ) | × | 2 25 | ( | 1 | − | 2 5 | ) | = | 0 |
方程左边 = | C | × | 21 | × | 2 25 | ( | 1 | − | 2 5 | ) |
= | C | × | 42 25 | ( | 1 | − | 2 5 | ) |
= | C | × | 42 25 | × | 1 | − | C | × | 42 25 | × | 2 5 |
= | C | × | 42 25 | − | C | × | 84 125 |
= | 126 125 | C |
126 125 | C | = | 0 |
C | = | 0 | ÷ | 126 125 |
= | 0 | × | 125 126 |
C | = | 0 |