ʱ : 黄冈中学2008届初三下摸底考试数学试题 - 百度文库ϿʼĶ
ɢٵãAB=220 ɢڵã110A90B=22200
C=110A=13200 D=90B=9000
Aʾ120Bʾ100Cʾ13200Dʾ9000 18⣺(1ССõֱΪAB
(2ƽ£
9ֽΪż(Ϊ¼M5ֽΪ(Ϊ¼N4ֽ
19(1֤OA
OA=ODDAƽ֡BDE
1=2=EDA AECD
EDAEAD=90㣬 1EAD=90㣮 AEǡOߣ
(2BDΪֱDBC=30 3=90㣭DBC=60
AD=2DE=2cm ߡ1=2=60㣬 AODΪΣ OD=AD=2cm BD=2OD=4cm
20⣺(1С2000140002%=2280(Ԫ Сţ1600110004%=2040(Ԫ
СС3·ݹʷֱ2280Ԫ2040Ԫ (2y2=kxb(17400(29200ã
y2=1800x5600
(3СΪy3СŹΪy4 y3=(1200x104002%2000=24x2208 y4=(1800x56004%1600=72x1824 y4y3x8
9·СŵĹʸСĹʣ
21⣺(1뾶ΪrԲΪO
OBOCABD OCAB RtOBDУ
Բİ뾶Ϊ3m
(2ȡһEEEGABGOOFEGEGӳFEG=1.70mGF=OD=0.7mEF=2.4m RtEOFУ 1.82=3.6(m
ĺΧΪ3.6m
22⣺(10x20ʱy=k1x(2060ãk1=3y=3x 20x40ʱy=k2xb(2060(400ã
(20x30ʱz=k3x(3060ã60=30k3k3=2z=2x
(3Ϊa0x20ʱa=3x2x=6x2 x=20ʱamax=2400
20x30ʱa=(3x1202x=6x2240x x=20ʱamax=2400
30x40ʱa=(3x12060=180x7200 x=30ʱamax=1800 ϣx=20ʱamax=2400
к20Ϊ2400Ԫ