A:to be decided
B:to have been decided
C:will be decided
D:have been decided
如图,已知椭圆 x2a2+y2b2=1 (a>b>0)的左右顶点分别是A(﹣ 2 ,0),B( 2 ,0),离心率为 22 .设点P(a,t)(t≠0),连接PA交椭圆于点C,坐标原点是O.
(Ⅰ)证明:OP⊥BC;
(Ⅱ)若三角形ABC的面积不大于四边形OBPC的面积,求|t|的最小值.
在匀速直线运动的速度公式v=st中,v的大小与S、t的大小无关,与该公式特征相似的还有( )
看图填空.
一共有____个图形.
三角形占____.
圆占____.
正方形占____.
长方形占____.
The fire started on the second floor and it wasn't long ______ the whole building was burned down.