2010届中考数学热点专题突破训练3.doc.doc

2010 中考数学热点专题突破训练――应用题 1.( 2009 南宁)、乙两个工程队参加竞标,甲工程队铺设广场砖的造价 y 甲(元) 与铺设面积?? 2mx 的函数关系如图 12 所示; 乙工程队铺设广场砖的造价 y 乙(元)与铺设面积?? 2mx 满足函数关系式: y kx ?乙. (1 )根据图 12 写出甲工程队铺设广场砖的造价 y 甲(元)与铺设面积?? 2mx 的函数关系式; (2 )如果狮山公园铺设广场砖的面积为 2 1600m ,那么公园应选择哪个工程队施工更合算? 解:(1 )当 0 500 x≤≤时,设 1 y k x ?甲,把?? 500 28000 , 代入上式得: 1 1 28000 28000 500 56 500 k k ? ???, 56 y x ? ?甲···································································································· 2分当500 x≥时,设 2 y k x b ? ?甲,把?? 500 28000 , 、?? 1000 48000 , 代入上式得: 22 500 28000 1000 48000 k b k b ? ???? ??······················································································ 3分解得: 240 8000 kb ?????···························································································· 4分 40 8000 y x ? ??甲???? 56 0 500 40 8000 500 x x y x x ???? ?????甲≤≥········································································· 5分(2 )当1600 x?时, 40 1600 8000 72000 y ? ???甲··········································· 6分 1600 y k ?乙···································································· 7分①当 y y ?乙甲时,即: 72000 1600 k?得:45 k?···································································································· 8分②当 y y ?乙甲时,即: 72000 1600 k?得: 0 45 k ? ?···········································