6.(5x-2y)•(2y-5x)的结果是( )
| A. | 25x2-4y2 | B. | 25x2-20xy+4y2 | C. | 25x2+20xy+4y2 | D. | -25x2+20xy-4y2 |
3.下列多项式不是完全平方式的是( )
0 278797 278805 278811 278815 278821 278823 278827 278833 278835 278841 278847 278851 278853 278857 278863 278865 278871 278875 278877 278881 278883 278887 278889 278891 278892 278893 278895 278896 278897 278899 278901 278905 278907 278911 278913 278917 278923 278925 278931 278935 278937 278941 278947 278953 278955 278961 278965 278967 278973 278977 278983 278991 366461
| A. | x2-4x-4 | B. | $\frac{1}{4}$+m2+m | C. | 9a2+6ab+b2 | D. | 4t2+12t+9 |