12.下列各运算中,计算正确的是( )
| A. | 2a•3a=6a | B. | a4÷a2=2 | C. | (2a2)3=8a6 | D. | (a+b)2=a2+b2 |
5.在有理数:-2,-(-2),|-2|,(-2)2,-(+2)中负数有( )
0 309768 309776 309782 309786 309792 309794 309798 309804 309806 309812 309818 309822 309824 309828 309834 309836 309842 309846 309848 309852 309854 309858 309860 309862 309863 309864 309866 309867 309868 309870 309872 309876 309878 309882 309884 309888 309894 309896 309902 309906 309908 309912 309918 309924 309926 309932 309936 309938 309944 309948 309954 309962 366461
| A. | 2个 | B. | 3个 | C. | 4个 | D. | 5个 |