ʱ : 【人教版】八年级下册数学《期末考试试题?附答? - 百度文库ϿʼĶ
𰸡22MN52
λ߶͵ֱεж֤PMNǵֱΣMN=ABʱBDС͵DBAӳʱBDзɣ ⡿ߵPMֱCDDEе㣬 PM=
2BDȻݵD21CEPMCE 21BDPNBD 2ߵPNֱDCBCе㣬 PN=
ߡABCADEΪֱΣ
AB=ACAD=AEBAC=DAE=90㣬 BAD=CAE ABDաACESAS BD=CE PM=PN
PMNǵΣ PMCE DPM=DCE PNBD PNC=DBC
ġߡDPN=DCB+PNC=DCB+DBC
MPN=DPM+DPN=DCE+DCB+DBC=BCE+DBC=ACB+ACE+DBC=ACB+ABD+DBC=ACB+ABC ߡBAC=90㣬
ACB+ABC=90㣬 MPN=90㣬
PMNǵֱΣ PM=PN=
1BD 2MN=
2BD 2DABʱBDС BD=AB-AD=4MNСֵ22 DBAӳʱBD BD=AB+AD=10MNֵΪ52 ߶MNȡֵΧ22MN52 ʴΪ22MN52
㾦תʣλ߶ȫεжʣֱεжʵȣؼǸȫεж͵ֱεж֤PMNǵΣ
20.
1ֽʽa2-b2+ac-bc
?2?x?1??x?1?2ⲻʽ?x?2x?3ʽ֮ͣ
?2?3?𰸡1a-ba+b+c20x36
1÷ֽⷨȷ飬ṫʽƽʽֽ⣬ṫʽa-bɽ 2ⲻʽ飬ҳ⣬ӿɽ ⡿1a2-b2+ac-bc =a2-b2+ac-bc =a+ba-b+ca-b =a-ba+b+c
?2?x?1??x?1?2?x?2x?3
??23?ⲻʽٵãx3 ⲻʽڵãx0
ʽĽ⼯Ϊ0x3 ʽΪ0123 Ϊ0+1+2+3=6
㾦ȡʽͷֽⷨʽֽ⡢ⲻʽ飬1ѵDz黹һ飬a2-b2÷ƽʽӦΪһ飬ac-bcṫʽΪһ飬2ĹؼȷʽĽ⼯
21.ͼıABCDУAB=CDDEACBFACֱΪEFDE=BF֤ 1AE=CF
2ıABCDƽıΣ
𰸡12
1ֱHL֤RtDECRtBFAɣ
2ȫεʽƽıεжó𰸣 ⡿֤1DEACBFAC DEC=BFA=90㣬
RtDECRtBFAУ?RtDECRtBFAHL EC=AF
EC-EF=AF-EFAE=FC 2RtDECRtBFA DCE=BAF
?AB?DC
?BF?DEABDC ֡AB=DC
ıABCDƽıΣ
㾦ҪȫεжԼƽıεжȷóRtDECRtBFAǽؼ
22.ʵabcmin|abc|ʾʵС磺min|-201|=-2
1-2
-3|=______min|35-x3x+6|=3xȡֵΧΪ______ 2x?13£2x+2+ڣ1xȡֵΧѡȡһʵֵ x?2x?21𰸡1-3-1x22x=0ʱԭʽ=1
x?11գmin|-20190-
1ָݵʺָݵʻ¶гʽ飬ԵõʽӵֵxȡֵΧ
2ݷʽļӷͳԻĿеʽӣȻݣ1xȡֵΧѡȡһʹԭʽ뻯ʽӼɽ⣮ ⡿1ߣ-20190=1-min|-20190-
1-2
=4 21-2
-3|=-3 2min|35-x3x+6|=3 ??5?x?3-1x2
?3x?6?3ʴΪ-3-1x2 2
x?13£x+2+ x?2x?2=
x?1?x?2??x?2??3 ?x?2x?2x?1x?2?2 x?2x?4?3=
=
x?1
?x?1??x?1?