Question

.随着世界气候大会于2009年12月7－18日在丹麦首都哥本哈根的召开，“低碳”概念风靡全球。在“低碳”理念的引领下，某市为实现森林城市建设的目标，在今年春季的绿化工作中，绿化办计划为某住宅小区购买并种植400株树苗，某树苗公司提供如下信息：

信息一：可供选择的树苗有雪松、香樟，垂柳三种，并且要求购买雪松、香樟的数量相等。

信息二：如下表：

设购买雪松，垂柳分别为x株、y株。

(1).写出y与x之间的函数关系式(不要求写出自变量的取值范围)；

(2).当每株垂柳的批发价P等于30元时，要使这400株树苗两年后对该住宅小区的空气净化指数不低于90，应怎样安排这三种树苗的购买数量，才能使购买树苗的总费用最低？最低的总费用是多少元？

(3).当每株垂柳批发价格P(元)与购买数量y(株)之间存在关系P＝30－0.05y时，求购买树苗的总费用W(元)与购买雪松数量x(株)之间的函数关系式(不要求写出自变量的取值范围)，并求出购买树苗总费用的最大值。

 

Answer 1

 （1） ·············································································································· 2分

（2）由题意得：   解得········································ 5分

0

当x=200时，=10000元························································································ 7分

（3）

       =···················································································· 9分

当x=175时，元··················································································· 10分

 

解析:略