Question

如圖所示，將矩形沿折疊，使點(diǎn)恰好落在上處，以為邊作正方形，延長(zhǎng)至，使，再以、為邊作矩形．

(1).試比較、的大小，并說(shuō)明理由．

(2).令，請(qǐng)問(wèn)是否為定值？若是，請(qǐng)求出的值；若不是，請(qǐng)說(shuō)明理由．

為定值．

(3).在（2）的條件下，若為上一點(diǎn)且，拋物線經(jīng)過(guò)、兩點(diǎn)，請(qǐng)求出此拋物線的解析式．

(4).在（3）的條件下，若拋物線與線段交于點(diǎn)，試問(wèn)在直線上是否存在點(diǎn)，使得以、、為頂點(diǎn)的三角形與相似？若存在，請(qǐng)求直線與軸的交點(diǎn)的坐標(biāo)；若不存在，請(qǐng)說(shuō)明理由．

 

 

 

 

 

 

 

 

 

 

 

Answer 1

解：（1），理由如下：

由折疊知：   在中，為斜邊 

故····························

（2）

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

（3），，

        

為等邊三角形，················································································ 4分

作于．      

  的坐標(biāo)為·································································· 5分

拋物線過(guò)點(diǎn)，，

   

所求拋物線解析式為········································································ 6分

（4）由（3）：

當(dāng)時(shí)，

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

方法1：若與相似，

而．則分情況如下

時(shí)為或····························· 8分

時(shí)    為或（0，1）······································ 9分

故直線與軸交點(diǎn)的坐標(biāo)為或或或（0，1）···············10分

方法2：與相似時(shí)，由（3）得則或，

過(guò)點(diǎn)作垂直軸于則或

當(dāng)時(shí)，

當(dāng) ，

， …………………10分

 

解析:略