17.下列说法错误的是( )
| A. | 四条边都相等的四边形是菱形 | |
| B. | 有三个角是直角的四边形是矩形 | |
| C. | 对角线互相垂直平分且相等的四边形是正方形 | |
| D. | 一组对边平行,另一组对边相等的四边形是等腰梯形 |
16.下列条件中,不能判断四边形ABCD是平行四边形的是( )
| A. | AB=CD,AD∥BC | B. | AB∥CD,AB=CD | C. | AB=CD,AD=BC | D. | AB∥CD,AD∥BC |
15.下列数中,0.4583,3.$\stackrel{•}{7}$,3.14,$\sqrt{2}$,$-\root{3}{8}$,$\frac{π}{2}$,0.373373337…是无理数的有( )
| A. | 2个 | B. | 3个 | C. | 4个 | D. | 5个 |
14.下列各式中正确的是( )
0 308776 308784 308790 308794 308800 308802 308806 308812 308814 308820 308826 308830 308832 308836 308842 308844 308850 308854 308856 308860 308862 308866 308868 308870 308871 308872 308874 308875 308876 308878 308880 308884 308886 308890 308892 308896 308902 308904 308910 308914 308916 308920 308926 308932 308934 308940 308944 308946 308952 308956 308962 308970 366461
| A. | $\sqrt{{{(-5)}^2}}$=-5 | B. | $\sqrt{8}=±2\sqrt{2}$ | C. | $\sqrt{48}=4\sqrt{3}$ | D. | ${(-\sqrt{2})^2}$=4 |