题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064103-87067.png)
每秒1个单位的速度向正方向运动,连结AP并延长,交抛物线于点B,分别过点A、B作x轴的垂线,垂
足为C、D,连结AQ、BQ.
(1)求抛物线的解析式;
(2)当A、Q、B三点构成以AQ为直角边的直角三角形时,求点P离开点Q多少时间?
(3)试探索当AP、AC、BP、BD与一个平行四边形的四条边对应相等(即这四条线段能构成平行四边形)时,点P离开点Q的时刻.
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064104-22846.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064103-87067.png)
∴c=
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064103-87067.png)
(2)①若AQ⊥BQ,过点Q作MN⊥y轴,
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064104-28255.png)
可证△AMQ∽△QNB.
∵AM=AC−MC=
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064104-42466.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064104-94055.png)
设B(3k,2k+
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064103-87067.png)
代入抛物线解析式得:k=
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064104-43752.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064105-62493.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064105-66383.png)
∴直线AB的解析式为:
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064105-89530.png)
∴OP=
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064105-47970.png)
②若AQ⊥AB,
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064106-30104.png)
∵AC∥PQ,可证△AMQ∽△QAP,
又由勾股定理得AQ=
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064106-41007.png)
∴PQ=
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064106-63641.png)
∴对应的时刻t为:2或
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064106-55970.png)
(3)①若AC=BD,AP=BP,
此时点A与点B关于y轴对称,
∴OP=AC=5,
∴PQ=4
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064103-87067.png)
②若AC=AP,
设P(0,y),则:9+(y−5)2=25,
解之得,y=1,即OP=1.
∴PQ=
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064103-87067.png)
此时,直线AP解析式为:
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064107-41758.png)
与抛物线的交点B为(
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064107-76626.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064107-83204.png)
∴PB=
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064107-67737.png)
∴满足条件的时刻为:
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064103-87067.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064103-87067.png)
解析
(2)分AQ⊥BQ, AQ⊥AB两种情况进行讨论;
(3)分AC=BD、AC=AP两种情况进行讨论。
核心考点
试题【如图,已知点A(−3,5)在抛物线y=x2+c的图象上,点P从抛物线的顶点Q出发,沿y轴以每秒1个单位的速度向正方向运动,连结AP并延长,交抛物线于点B,分别过】;主要考察你对二次函数定义等知识点的理解。[详细]
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064100-95000.jpg)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064056-39636.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064057-21992.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064057-95465.png)
(1)点C的坐标为( , );
(2)若二次函数
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064046-86638.png)
①求二次函数
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064046-86638.png)
②当-1≤x≤4时,直接写出函数值y对应的取值范围;
③在此二次函数的图象上是否存在点P(点C除外),使△ABP是以AB为直角边的等腰直角三角形?若存在,求出所有点P的坐标;若不存在,请说明理由.
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064046-92759.jpg)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064031-91213.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064031-28713.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064031-79940.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064032-55415.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064032-53920.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064032-70511.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064032-65785.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064032-26259.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064033-82335.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064033-68125.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064033-14147.png)
(1)写出
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064033-59751.png)
(2)判断
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064034-20335.png)
(3)在线段
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064034-78879.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064034-54382.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064034-11980.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064034-51396.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064034-54382.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191019/20191019064027-44684.png)
(1)写出点B的坐标 ;
(2)已知点P是二次函数y=-x2+3x图象在y轴右侧部分上的一个动点,将直线y=-2x沿y轴向上平移,分别交x轴、y轴于C、D两点. 若以CD为直角边的△PCD与△OCD相似,则点P的坐标为 .
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