圈圈背影
花朵
共回答了17个问题采纳率:94.1% 举报
小题1:对于
![](https://img.yulucn.com/upload/e/56/e5620c0045652e14a888fbdd5d7b4e85_thumb.jpg)
,令x=0,得y=4,即B(0,4);…
令y=0,即
![](https://img.yulucn.com/upload/1/a8/1a87dd374217deba0aad895918c447d7_thumb.jpg)
,解得:x
1 = —2,x
2 = 4,即A(4,0)
设直线AB的解析式为y =" kx" + b,
把A(4,0),B(0,4)分别代入上式,得
![](https://img.yulucn.com/upload/f/62/f623acc06f1552fc21738e02a96908f7_thumb.jpg)
,解得:k = —1,b = 4,
∴直线AB的解析式为y = —x + 4。
小题1:当点P(x,y)在直线AB上时,由x = —x + 4,得:x = 2,
当点Q在直线AB上时,依题意可知Q(
![](https://img.yulucn.com/upload/9/7a/97a99183a3246fd2d884da5cf5e86930_thumb.jpg)
,
![](https://img.yulucn.com/upload/8/c4/8c4985ab50c28a9c0240a50ef8f5dcb9_thumb.jpg)
),由
![](https://img.yulucn.com/upload/d/71/d7154a4c78dfbd4ff5b7720dd8501606_thumb.jpg)
,得:x = 4,
∴若正方形PEQF与直线AB有公共点,则x的取值范围为2≤x≤4;
小题1:当点E(x,
![](https://img.yulucn.com/upload/9/7a/97a99183a3246fd2d884da5cf5e86930_thumb.jpg)
)在直线AB上时,
![](https://img.yulucn.com/upload/1/7b/17bcc6091971a2f75604a28295335695_thumb.jpg)
,解得
![](https://img.yulucn.com/upload/f/16/f16a4ca6f663b6f790a4c44d5ec6f11a_thumb.jpg)
,
①当
![](https://img.yulucn.com/upload/c/14/c14e42c9703b99e6995f6ec58cf32062_thumb.jpg)
时,直线AB分别与PE、PF交于点C、D,此时PC = x—(—x+4) = 2x—4,
∵ PD = PC,
∴ S
△ PCD =
∴
∵
![](https://img.yulucn.com/upload/f/f6/ff6a31d226cdfee845be6d65ff667288_thumb.jpg)
,
∴当
![](https://img.yulucn.com/upload/1/94/194deec07048360eecab37e680b3be98_thumb.jpg)
时,
②当
![](https://img.yulucn.com/upload/a/86/a865f0efaa4f0a5ee49e02beffb1cd0e_thumb.jpg)
时,直线AB分别与QE、QF交于点M、N,此时,
∵ QM = QN,
∴ S
△ QMN =
即
![](https://img.yulucn.com/upload/c/35/c35ff54d1a82d56ba68895e7c05ab34f_thumb.jpg)
,
其中,当
![](https://img.yulucn.com/upload/f/16/f16a4ca6f663b6f790a4c44d5ec6f11a_thumb.jpg)
时,
综合①、②,当
![](https://img.yulucn.com/upload/1/94/194deec07048360eecab37e680b3be98_thumb.jpg)
时,
小题1:抛物线的解析式中,令x=0可求出B点的坐标,令y=0可求出A点的坐标,然后用待定系数法即可求出直线AB的解析式;
小题1:可分别求出当点P、点Q在直线AB上时x的值,即可得到所求的x的取值范围;
小题1:此题首先要计算出一个关键点:即直线AB过E、F时x的值(由于直线AB与直线OP垂直,所以直线AB同时经过E、F),此时点E的坐标为(x,
![](https://img.yulucn.com/upload/f/83/f83cb8124e4fe234ffcf088453f6b831_thumb.jpg)
),代入直线AB的解析式即可得到x=
![](https://img.yulucn.com/upload/b/7c/b7cd6c4adfad464a516524042b5af3b1_thumb.jpg)
;
①当2≤x<
![](https://img.yulucn.com/upload/b/7c/b7cd6c4adfad464a516524042b5af3b1_thumb.jpg)
时,直线AB与PE、PF相交,设交点为C、D;那么重合部分的面积为正方形QEPF和等腰Rt△PDC的面积差,由此可得到关于S、x的函数关系式,进而可根据函数的性质及自变量的取值范围求出S的最大值及对应的x的值;
②当
![](https://img.yulucn.com/upload/b/7c/b7cd6c4adfad464a516524042b5af3b1_thumb.jpg)
≤x≤4时,直线AB与QE、QF相交,设交点为M、N;此时重合部分的面积为等腰Rt△QMN的面积,可参照①的方法求出此时S的最大值及对应的x的值;
综合上述两种情况,即可比较得出S的最大值及对应的x的值.
1年前
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