-1-海淀区2018年八年级学业发展水平评价数学答案2018.7一、选择题(本题共30分,每小题3分)题号12345678910答案CADAABCBAD二、填空题(本题共18分,每小题3分)11.512.213.>14.乙15.22364xx16.3;mn.(前空2分后空1分)三、解答题(本题共22分,第17—19题每小题4分,第20—21题每小题5分)17.解:原式12222-----------------------------------------------------------------------------2分122-----------------------------------------------------------------------------------------3分1---------------------------------------------------------------------------------------------------4分另解:原式118222---------------------------------------------------------------------------1分21-----------------------------------------------------------------------------------------3分1---------------------------------------------------------------------------------------------------4分18.证法一: □ABCD,∴AD∥BC,AD=BC,------------------------------1分∴12=,∴34.-----------------------------------------------2分 BEDF,∴ADFCBE△≌△,-----------------------------------3分∴AFCE.----------------------------------------------4分说明:由证ABFCDE△≌△获得结论,对应上述证法相应步骤给分.证法二:连接AC交BD于点O,连接AE,CF. 四边形ABCD为平行四边形,∴OAOC,OBOD.----------------------------1分 BEDF,∴ODDFOBBE,即OFOE.-------------------------------------------------2分4321FEDCBAOABCDEF-2-xy-624l2l1ABO213EDCFBA∴四边形AECF是平行四边形.--------------------------------------------------------------3分∴AFCE.--------------------------------------------------------------------------------------4分19.解法一:222xxyyxyxy.---------------------------------------------------------------1分 23x,23y,∴原式223232323161-------------------------------------------------------------------------------------3分15.----------------------------------------------------------------------------------------4分解法二: 23x,23y,∴原式222323232374343744---------------------------------------------------------3分15.----------------------------------------------------------------------------------------4分20.解:(1) 点B(m,4)在直线2l:2yx上,∴2m.-----------------------------------------------------------------------------------------1分设直线1l的解析式为ykxb. 直线1l过点A(6,0),B(2,4),∴0642kbkb,,-------------------2分∴123kb,,∴直线1l的解析式为132yx.-----------------------------------------------------------3分(2)2n.---------------------------------------------------------------------------------------------5分21.(1)证明: 四边形ABCD为平行四边形,∴AD∥BC.------------------------------1分∴12=. BE平分ABC,∴13=.∴23=.∴ABAE.---------------------------------------------------------------------------------2分 ABBF,∴AEBF.-3-GEDCFBA∴四边形ABFE是平行四边形.∴四边形ABFE是菱形.-------------------------------------------------------------------3分(2)过点A作AG⊥BC于点G.∴90ABG°. 4AB,60ABC°,∴2BG,23AG.-----------------------4分 4BFAB==,∴83ABFESBFAG菱形.-----------------------------------------------------...