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已知點A(a.).B(2a.y).C(3a.y)都在拋物線上. (1)求拋物線與x軸的交點坐標(biāo), (2)當(dāng)a=1時.求△ABC的面積, (3)是否存在含有.y.y.且與a無關(guān)的等式?如果存在.試給出一個.并加以證明,如果不存在.說明理由. 解:(1)由5=0.·············································································· 得.．·················································································· ∴拋物線與x軸的交點坐標(biāo)為(0.0).(.0)．······································· (2)當(dāng)a=1時.得A.B.C.······························ 分別過點A.B.C作x軸的垂線.垂足分別為D.E.F.則有 =S - - ···················································· =--···································· =5········································································ (3)如:． ········································································· 事實上. =45a2+36a． 3()=3[5×(2a)2+12×2a-(5a2+12a)] =45a2+36a．············ ∴． ···················································································· 【查看更多】

 

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一張試卷25題，若做對了一題得4分，做錯了一題扣1分，小李做完此卷后得70分，則他做對的題目數(shù)是（　　）
A、18B、17C、19D、20

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21、有一益智游戲分二階段進行，其中第二階段共有25題，答對一題得3分，答錯一題扣2分，不作答得0分．若小明已在第一階段得50分，且第二階段答對了20題，則下列哪一個分數(shù)可能是小明在此益智游戲中所得的總分（　�。�

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2、本卷第17～25題的9道題中，每道題所賦分數(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、一張試卷上有25道選擇題：對一道題得4分，錯一道得-1分，不做得-1分，某同學(xué)做完全部25題得70分，那么它做對題數(shù)為（　�。�

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一本練習(xí)冊內(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)冊中有25題的練習(xí)卷的份數(shù)為（　�。�
A、1B、2C、3D、4

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