解得：x1?9，x2??21（不符合实际情况，舍去） ·························································· 6分 当x?9时，4x?36，50?3x?77
∴当两人相距85m时，甲在O点以东36m处，乙在O点以北77m处． ·························· 8分 解法2：设甲与O处的距离为xm时，两人相距85m 则乙与O处的距离为?2222222?3?······················································································ 1分 x?50?m ·
4???3?x??x?50??852 ·········································································································· 4分
?4?2解得：x1?36，x2??84（不符合实际情况，舍去 ） ······················································ 6分 当x?36，x?50?77 ········································································································· 7分 答：当两人相距85米时，甲在O点以东36米处，乙在O点以北77米处． ···················· 8分 21．（8分）证明： ∵∠1=∠B
∴∠AED=2∠B，DE=BE ········································································································ 2分 ∴∠C=∠AED ························································································································· 3分 在△ACD和△AED中
34??CAD??EAD? ?AD?AD??C??AED?∴△ACD≌△AED ··················································································································· 5分
∴AC=AE，CD=DE，∴CD=BE． ·························································································· 6分 ∴AB=AE+EB=AC+CD． ········································································································· 8分 22．（9分）解：（1）设最多可购买乙树苗x棵，则购买甲树苗（600?x??）棵 ················ 1分 ································································································ 3分 60(600?x)?80x≤44000 ·
x≤400．
答：最多可购买乙树苗400棵． ···························································································· 5分 （2）设购买树苗的费用为y 则y?60(600?x)?80x
y?20 ················································································································ 6分 x?36000根据题意 0.88(600?x)?0.96x≥0.9?600
x≥150
∴当x?150时，y取最小值． ······························································································ 8分 ymin?20?150?36000
?39000．
答：当购买乙树苗150棵时费用最低，最低费用为39000元． ·········································· 9分 （本题不答不扣分） 23．（10分）解：（1）所作菱形如图①、②所示．
说明：作法相同的图形视为同一种．例如类似图③、图④的图形视为与图②是同一种．
（作出一个图形得3分） （2）图①的作法：
作矩形A1B1C1D1四条边的中点E1、F1、G1、H1； 连接H1E1、E1F1、G1F1、G1H1． 四边形E1F1G1H1即为菱形． 图②的作法：
在B2C2上取一点E2，使E2C2＞A2E2且E2不与B2重合； 以A2为圆心，A2E2为半径画弧，交A2D2于H2；
以E2为圆心，A2E2为半径画弧，交B2C2于F2； 连接H2F2，则四边形A2E2F2H2为菱形． （写对一个作法得2分）
（此题答案不惟一，只要画法及作法合理、正确，均可酌情得分．） 24．（10分）解：（1）设抛物线的表达式为y?ax ····· 1分 点B(6，?5.6)在抛物线的图象上． ∴?5.6?36a
27 ·········································································· 3分 4572∴抛物线的表达式为y??························································································· 4分 x ·
45a??（2）设窗户上边所在直线交抛物线于C、D两点，D点坐标为（k，t）
已知窗户高1.6m，∴t??5.6?(?1.6)??4 ······································································· 5分