3.3+1.67=____
2.4×5=____
6.3÷0.03=____
14 + 13 =____
37 × 17 =____
0.31÷3.1=____
18 +0.375=____
1÷ 18 =____
15﹣ 815 ﹣ 715 =____
一质量为1.5kg的小球从斜面上滚下,如图所示.试在图中画出
如图,已知AF⊥平面ABCD,四边形ABEF为矩形,四边形ABCD为直角梯形,∠DAB=90°,AB∥CD,AD=AF=CD=2,AB=4.
(1)求证:AF∥平面BCE;
(2)求证:AC⊥平面BCE;
(3)求三棱锥E﹣BCF的体积.