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《山西省2018-2019学年第一学期八年级阶段三质量评估试题·数学(人教版)·答案.pdf》由会员上传分享,免费在线阅读,更多相关内容在行业资料-天天文库。
1、19.解:小亮说的对.!!!!!!!!!!!!!!!!!!!!!!!!2分山西省2018-2019学年第一学期八年级阶段三质量评估试题理由如下:23(x+1)-(6x-5)-2(x-2)(x+2)数学(人教版)参考答案和评分标准22=3(x+2x+1)-6x+5-2(x-4)!!!!!!!!!!!!!!!!!!!!4分22=3x+6x+3-6x+5-2x+8!!!!!!!!!!!!!!!!!!!!!!5分一、选择题(每小题3分,共30分)2=x+16.!!!!!!!!!!!!!!!!!!!!!!!!!!!!6分题号1234567891021165选项ADBCCBDCDC当x
2、=时,原式= +16=;!!!!!!!!!!!!!!!!!7分224二、填空题(每小题3分,共15分)11265当x=-时,原式= - +16=.!!!!!!!!!!!!!!!!8分2242211.2(x-3)12.-1613.2a(a+b)或2a+2ab14.415.6∴小亮说的对.!!!!!!!!!!!!!!!!!!!!!!!!!9分三、解答题(本大题共8小题,共75分)20.解:(1)∵点D是BC边的中点,DE⊥BC,22216.解:(1)原式=[xy(xy-1)-xy(1-xy)]÷xy-2xy!!!!!!!!!!!!2分∴PB=PC.22=[xy(2xy-2)]
3、÷xy-2xy!!!!!!!!!!!!!!!!3分∴∠PBC=∠PCB.!!!!!!!!!!!!!!!!!!!!!!!!!1分=2xy-2-2xy!!!!!!!!!!!!!!!!!!!!!4分∵BP平分∠ABC,∴∠PBC=∠ABP.!!!!!!!!!!!!!!!!!!!!!!!!2分=-2.!!!!!!!!!!!!!!!!!!!!!!!!!5分∴∠PBC=∠PCB=∠ABP.!!!!!!!!!!!!!!!!!!!!!3分222(2)原式=4x-9+x-4x+4-4x+4x!!!!!!!!!!!!!!!!!!8分∵∠A=60°,∠ACP=24°,2=x-5.!!!!!!!!
4、!!!!!!!!!!!!!!!!!9分∴∠PBC+∠PCB+∠ABP=180°-60°-24°=96°.2当x=-2时,原式=(-2)-5=4-5=-1.!!!!!!!!!!!!!!!!10分∴3∠ABP=96°.17.解:(1)-9025!!!!!!!!!!!!!!!!!!!!!!!!!!2分∴∠ABP=32°.!!!!!!!!!!!!!!!!!!!!!!!!!!4分(2)由题意得,这两个数分别为(10a+b)和(10a+10-b),!!!!!!!!!4分(2)由(1)得∠PBC=∠PCB=∠ABP=β.!!!!!!!!!!!!!!!6分22(10a+b)(10a+10-
5、b)=100a+100a+10b-b=100a(a+1)+b(10-b).!!!!!7分∵∠A=60°,∠ACP=α,2218.解:(1)原式=-3a(a-4ab+4b)!!!!!!!!!!!!!!!!!!!3分∴∠PBC+∠PCB+∠ABP=120°-α.!!!!!!!!!!!!!!!!!!7分=-3a(a-2b)2%.%%%%%%%!!!!!!!!!!!!!!!!!!!!!5分∴3∠ABP=120°-α.2(2)原式=m+8m-9-8m!!!!!!!!!!!!!!!!!!!!!!7分∴3β+α=120°.2=m-9!!!!!!!!!!!!!!!!!!!!!!!!!9分即
6、α,β满足的关系式为α+3β=120°.!!!!!!!!!!!!!!!!8分=(m+3)(m-3).!!!!!!!!!!!!!!!!!!!!!10分八年级数学(人教版)答案第1页(共4页)八年级数学(人教版)答案第2页(共4页)n(n+1)2223.解:(1)30°!!!!!!!!!!!!!!!!!!!!!!!!!!!2分21.解:(1)×8+1=4n+4n+1=(2n+1),2(2)S1和S2的数量关系是S1=S2.!!!!!!!!!!!!!!!!!!!4分即:任意一个三角形数乘8再加1是一个完全平方数.!!!!!!!!!4分理由如下:n(n+1)(n+1)(n+2)(2
7、)设第n个三角形数为,则第(n+1)个三角形数为,22如图3,分别作AC,EC边上的高DM,BN,n(n+1)(n+1)(n+2)(n+1)(2n+2)2DM交AC于点M,BN交EC的延长线于点N.!!!!!!!!!!!!5分这两个数的和为+==(n+1),222E即:连续两个三角形数的和是一个完全平方数.!!!!!!!!!!!10分22.解:(1)如图所示.!!!!!!!!!!!!!!!!!!!!!!!!!!2分DDCEMNABA图3∵Rt△ABC≌Rt△EDC,BC∴EC=AC,CD=CB.!!!!!!!!!!
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