A:become
B:turned
C:come
D:changed
抛物线x2=4y的焦点坐标是( )
如图(1),在四边形ABCD中,对角线AC⊥BD,垂足为点P.求证:S四边形ABCD= 12 AC•BD;
证明:∵AC⊥BD,
∴ {S△ACD=12AC⋅PDS△ABC=12AC⋅BP
∴S四边形ABCD=S△ACD+S△ACB= 12 AC•PD+ 12 AC•BP
= 12 AC(PD+PB)= 12 AC•BD
解答问题:
Don't forget ________ the door when you leave the room.
坚强的意志能促使人的潜能得到充分的开发,能使人积极地迎接挑战。下列能充分说明这一道理的是( )