Question

 

如图所示，将矩形沿折叠，使点恰好落在上处，以为边作正方形，延长至，使，再以、为边作矩形．

(1). （2分）试比较、的大小，并说明理由．

2）令，请问是否为定值？若是，请求出的值；若不是，请说明理由．

 

3在（2）的条件下，若为上一点且，抛物线经过、两点，请求出此抛物线的解析式．

(4).在（3）的条件下，若抛物线与线段交于点，试问在直线上是否存在点，使得以、、为顶点的三角形与相似？若存在，请求直线与轴的交点的坐标；若不存在，请说明理由．

 

 

Answer 1

 

 

(1). （2分）试比较、的大小，并说明理由．

（1），理由如下：

由折叠知：   在中，为斜边 

故·················································································································2分

 (2). （1分）令，请问是否为定值？若是，请求出的值；若不是，请说明理由．

为定值．

····································································································3分

 (3).在（2）的条件下，若为上一点且，抛物线经过、两点，请求出此抛物线的解析式．

，，

        

为等边三角形，················································································4分

作于．      

  的坐标为··································································5分

抛物线过点，，

   

所求抛物线解析式为········································································6分

 

 

(4).在（3）的条件下，若抛物线与线段交于点，试问在直线上是否存在点，使得以、、为顶点的三角形与相似？若存在，请求直线与轴的交点的坐标；若不存在，请说明理由．

由（3）：

当时，

··························································7分

方法1：若与相似，

而．则分情况如下

时    为或····························· 8分

时    为或（0，1）······································ 9分

故直线与轴交点的坐标为或或或（0，1）··············· 10分

方法2：与相似时，由（3）得则或，

过点作垂直轴于则或

当时，

当  ，

， …………………10分

 

解析:略