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如圖.在平面直角坐標(biāo)系中.拋物線=-++經(jīng)過(guò)A.B(.0). C(.0)三點(diǎn).且-=5． (1)求.的值, (2)在拋物線上求一點(diǎn)D.使得四邊形BDCE是以BC為對(duì) 角線的菱形, (3)在拋物線上是否存在一點(diǎn)P.使得四邊形BPOH是以O(shè)B為對(duì)角線的菱形?若存在.求出點(diǎn)P的坐標(biāo).并判斷這個(gè)菱形是否為正方形?若不存在.請(qǐng)說(shuō)明理由． 解:(1)解法一: ∵拋物線=-++經(jīng)過(guò)點(diǎn)A. ∴=-4 --1分 又由題意可知..是方程-++=0的兩個(gè)根. ∴+=. =-=6··································································· 2分 由已知得(-)=25 又(-)=(+)-4=-24 ∴ -24=25 解得=± ··········································································································· 3分 當(dāng)=時(shí).拋物線與軸的交點(diǎn)在軸的正半軸上.不合題意.舍去． ∴=-． ·········································································································· 4分 解法二:∵.是方程-++c=0的兩個(gè)根. 即方程2-3+12=0的兩個(gè)根． ∴=.··········································································· 2分 ∴-==5. 解得 =±······························································································· 3分 (2)∵四邊形BDCE是以BC為對(duì)角線的菱形.根據(jù)菱形的性質(zhì).點(diǎn)D必在拋物線的對(duì)稱軸上. 5分 又∵=---4=-(+)+ ································· 6分 ∴拋物線的頂點(diǎn)(-.)即為所求的點(diǎn)D．······································· 7分 (3)∵四邊形BPOH是以O(shè)B為對(duì)角線的菱形.點(diǎn)B的坐標(biāo)為. 根據(jù)菱形的性質(zhì).點(diǎn)P必是直線=-3與 拋物線=---4的交點(diǎn). ···························································· 8分 ∴當(dāng)=-3時(shí).=-×(-3)-×(-3)-4=4. ∴在拋物線上存在一點(diǎn)P.使得四邊形BPOH為菱形． ·················· 9分 四邊形BPOH不能成為正方形.因?yàn)槿绻倪呅蜝POH為正方形.點(diǎn)P的坐標(biāo)只能是.但這一點(diǎn)不在拋物線上．······································································································· 10分 【查看更多】

 

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一本練習(xí)冊(cè)內(nèi)有24份練習(xí)卷，總共有426道練習(xí)題，每份練習(xí)卷中有25題或20題或16題．那么這本練習(xí)冊(cè)中有25題的練習(xí)卷的份數(shù)為（　�。�
A、1B、2C、3D、4

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一張?jiān)嚲?5題，若做對(duì)了一題得4分，做錯(cuò)了一題扣1分，小李做完此卷后得70分，則他做對(duì)的題目數(shù)是（　　）
A、18B、17C、19D、20

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2、本卷第17～25題的9道題中，每道題所賦分?jǐn)?shù)（注：分值依次為6，7，7，8，8，8，9，9，10）的眾數(shù)和中位數(shù)分別是（　�。�

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9、一張?jiān)嚲砩嫌?5道選擇題：對(duì)一道題得4分，錯(cuò)一道得-1分，不做得-1分，某同學(xué)做完全部25題得70分，那么它做對(duì)題數(shù)為（　�。�

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21、有一益智游戲分二階段進(jìn)行，其中第二階段共有25題，答對(duì)一題得3分，答錯(cuò)一題扣2分，不作答得0分．若小明已在第一階段得50分，且第二階段答對(duì)了20題，則下列哪一個(gè)分?jǐn)?shù)可能是小明在此益智游戲中所得的總分（　�。�

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