7.下列各式中,不能用平方差公式计算的是( )
| A. | (-x-y)(x-y) | B. | (x-y)(-x+y) | C. | (x+y)(-x+y) | D. | (-x+y)(-x-y) |
6.下列各式中,计算正确的是( )
0 307751 307759 307765 307769 307775 307777 307781 307787 307789 307795 307801 307805 307807 307811 307817 307819 307825 307829 307831 307835 307837 307841 307843 307845 307846 307847 307849 307850 307851 307853 307855 307859 307861 307865 307867 307871 307877 307879 307885 307889 307891 307895 307901 307907 307909 307915 307919 307921 307927 307931 307937 307945 366461
| A. | (a3)2=a6 | B. | a8÷a2=a4 | C. | a3•a2=a6 | D. | a+2a2=3a2 |