19.
如图,菱形ABCD的周长为32,∠C=120°,AE⊥BC,AF⊥CD,垂足为别为E、F,连结EF,则△AEF的面积是( )
| A. | 8 | B. | $8\sqrt{3}$ | C. | $12\sqrt{3}$ | D. | $16\sqrt{3}$ |
16.
如图,直线a∥b,直线c分别与直线a,b相交于点A,B,且AC垂直直线c于点A,若∠1=40°,则∠2的度数为( )
| A. | 140° | B. | 90° | C. | 50° | D. | 40° |
15.下列命题中,假命题是( )
0 285458 285466 285472 285476 285482 285484 285488 285494 285496 285502 285508 285512 285514 285518 285524 285526 285532 285536 285538 285542 285544 285548 285550 285552 285553 285554 285556 285557 285558 285560 285562 285566 285568 285572 285574 285578 285584 285586 285592 285596 285598 285602 285608 285614 285616 285622 285626 285628 285634 285638 285644 285652 366461
| A. | 如果两条直线都与第三条直线平行,那么这两条直线也互相平行 | |
| B. | 在同一平面内,过一点有且只有一条直线与已知直线垂直 | |
| C. | 两条直线被第三条直线所截,同旁内角互补 | |
| D. | 两直线平行,内错角相等 |