19.已知四边形ABCD中,AB与CD不平行,AC与BD相交于点O,那么下列条件中能判定四边形ABCD是等腰梯形的是( )
| A. | AC=BD=BC | B. | AB=AD=CD | C. | OB=OC,AB=CD | D. | OB=OC,OA=OD |
18.
如图,在△ABC中,∠A=90°,AB=AC=6,点D是BC中点,点E、F分别在AB、AC上,且BE=AF,则四边形AEDF的面积为( )
| A. | 6 | B. | 7 | C. | 6$\sqrt{2}$ | D. | 9 |
13.
如图,在菱形纸片ABCD中,∠A=60°,点E在BC边上,将菱形纸片ABCD沿DE折叠,点C落在AB边的垂直平分线上的点C′处,则∠DEC的大小为( )
0 286080 286088 286094 286098 286104 286106 286110 286116 286118 286124 286130 286134 286136 286140 286146 286148 286154 286158 286160 286164 286166 286170 286172 286174 286175 286176 286178 286179 286180 286182 286184 286188 286190 286194 286196 286200 286206 286208 286214 286218 286220 286224 286230 286236 286238 286244 286248 286250 286256 286260 286266 286274 366461
| A. | 30° | B. | 45° | C. | 60° | D. | 75° |