18.在0,π,$\frac{2}{3}$,$\sqrt{2}$,-$\sqrt{9}$中,无理数的个数是( )
| A. | 1个 | B. | 2个 | C. | 3个 | D. | 4个 |
17.在?ABCD中,对角线AC、BD相交于点O,若AC=8,BD=6,AB=5,则△AOB的周长为( )
| A. | 11 | B. | 12 | C. | 13 | D. | 14 |
16.
如图,在△ABC中,点E、F分别是AB、AC的中点,则下列结论不正确的是( )
0 284739 284747 284753 284757 284763 284765 284769 284775 284777 284783 284789 284793 284795 284799 284805 284807 284813 284817 284819 284823 284825 284829 284831 284833 284834 284835 284837 284838 284839 284841 284843 284847 284849 284853 284855 284859 284865 284867 284873 284877 284879 284883 284889 284895 284897 284903 284907 284909 284915 284919 284925 284933 366461
| A. | EF∥BC | B. | BC=2EF | C. | ∠AEF=∠B | D. | AE=AF |