3.
已知:如图,在△ABC中,AB=AC,DE是AB的垂直平分线,若BE+CE=12,BC=8,则△ABC的周长为( )
| A. | 20 | B. | 32 | C. | 24 | D. | 36 |
19.
对四边形ABCD加条件,使之成为平行四边形,下面的添加不正确的是( )
| A. | AB=CD,AB∥CD | B. | AB∥CD,AD=BC | C. | AB=CD,AD=BC | D. | AC与BD相互平分 |
16.
如图,?ABCD中,∠C=120°,AB=AE=5,AE与BD交于点F,AF=2EF,则BC的长为( )
| A. | 6 | B. | 8 | C. | 10 | D. | 12 |
15.下列方程组中,是二元一次方程组的是( )
0 297723 297731 297737 297741 297747 297749 297753 297759 297761 297767 297773 297777 297779 297783 297789 297791 297797 297801 297803 297807 297809 297813 297815 297817 297818 297819 297821 297822 297823 297825 297827 297831 297833 297837 297839 297843 297849 297851 297857 297861 297863 297867 297873 297879 297881 297887 297891 297893 297899 297903 297909 297917 366461
| A. | $\left\{\begin{array}{l}\frac{1}{3}x-5y=1\\ 6xy=7\end{array}\right.$ | B. | $\left\{\begin{array}{l}5x-y=2\\ y=4x+1\end{array}\right.$ | ||
| C. | $\left\{\begin{array}{l}3{x^2}-x-3=0\\ y=x-1\end{array}\right.$ | D. | $\left\{\begin{array}{l}\frac{2}{x}-1=y\\ 4x+y=0\end{array}\right.$ |