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30．已知:如圖14.拋物線與軸交于點.點.與直線相交于點.點.直線與軸交于點． (1)寫出直線的解析式． (2)求的面積． (3)若點在線段上以每秒1個單位長度的速度從向運動(不與重合).同時.點在射線上以每秒2個單位長度的速度從向運動．設(shè)運動時間為秒.請寫出的面積與的函數(shù)關(guān)系式.并求出點運動多少時間時.的面積最大.最大面積是多少? 解:(1)在中.令 . .··············································· 1分 又點在上 的解析式為·············································································· 2分 (2)由.得 ···················································· 4分 . .······························································································· 5分 ························································································· 6分 (3)過點作于點 ······························································································· 7分 ·········································································································· 8分 由直線可得: 在中...則 .······················································································· 9分 ···················································································· 10分 ····························································································· 11分 此拋物線開口向下.當時. 當點運動2秒時.的面積達到最大.最大為．···························· 12分 【查看更多】

 

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27、在一次數(shù)學(xué)知識競賽中，競賽題共30題．規(guī)定：答對一道題得4分，不答或答錯一道題倒扣2分，得分不低于60分者得獎．得獎?wù)咧辽賾?yīng)答對
20
道題．

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一次數(shù)學(xué)競賽共30題，每題給出4個答案，期中只有一個正確，要求學(xué)生將正確答案選出來，每道題選對得4分，不選或選錯倒扣1分．
（1）小明在這次競賽中得了80分，問他選對了多少題？
（2）這時，小高過來對小明說，自己在這次競賽中得了92分，請問小高的話可信嗎？說明理由．

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6、下列各數(shù)中，屬于科學(xué)記數(shù)法的是（　　）

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（2008•漳州）在一次數(shù)學(xué)知識競賽中，競賽題共30題．規(guī)定：答對一道題得4分，不答或答錯一道題倒扣2分，得分不低于60分者得獎．得獎?wù)咧辽賾?yīng)答對    道題．

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一次數(shù)學(xué)競賽共30題，每題給出4個答案，期中只有一個正確，要求學(xué)生將正確答案選出來，每道題選對得4分，不選或選錯倒扣1分．
（1）小明在這次競賽中得了80分，問他選對了多少題？
（2）這時，小高過來對小明說，自己在這次競賽中得了92分，請問小高的話可信嗎？說明理由．

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