已知F是双曲线x2-y28=1的右焦点，A(-2，3)，P是双曲线右支上的动点，_爱下问搜题

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问题选择题

已知F是双曲线x2-

y2

8

=1的右焦点，A(-2，

3

)，P是双曲线右支上的动点，则|PA|-|PF|的最小值为（　　）

A．0

B．2

C．4

D．6

答案

如图，设双曲线x2-

y2

8

=1的左焦点为F₁，

当直线F₁A与双曲线x2-

y2

8

=1右半轴的交点为P时，

|PA|-|PF|取最小值，

∵F₁（-3，0），A（-2，

3

），

∴|AF₁|=

(-3+2)2+(

3

)2

=2，

∵|PF₁|-|PF|=2a=2，

∴|PA|-|PF|=|PF₁|-|PF|-|AF₁|=2-2=0．

∴|PA|-|PF|的最小值为0．

故选A．

完形填空

I was fifteen months old, a happy kid until the day I fell. It was a    31   fall. I landed on a glass rabbit which cut my eye badly enough to make it blind. Trying to save the eye, the doctors stitched(缝合) the eyeball together where it was    32  , leaving a big ugly scar(疤痕) in the middle of my eye. The attempt    33  , but my mother, in all of her wisdom, found another doctor who knew that if the eye were removed    34  , my face would grow up badly distorted(扭曲)，   35   my scarred, sightless, cloudy and gray eye lived on with me. As I grew, this sightless eye in so many ways    36   me.
I walked with my face looking at the    37   so that people would not see the    38   me. Yet my mother would say to me, at every turn, “Hold your head up high and    39   the world. If you hold your head up high, it will be OK, and people will see your    40   soul.” She continued this    41   whenever I was trying to hide.
Mama’s words were of great help for me to face the world    42  . As a teenager, even though I tended to look down to hide my shame, I found that sometimes when I held my head up high and let people know me, they    43   me. In high school, I was    44   both academically and socially. I was    45   elected class president. My mother’s words helped me begin to realize that by letting people look at my face, I let them    46   the intelligence and beauty behind both eyes, even if they couldn’t see it on the    47  .
Now I’m a happy wife and great mother. The message “Hold your head up high,” has been
   48   many times in my   49   home. Each of my children has felt    50   invitation, and the gift my mother gave me has lived on in another generation.

D．interrupted

A．comfortable

选择题

马克思说：“宪法是法律的法律。”这句话说明[ ]

A．宪法包含着普通法律

B．普通法律是宪法的重要组成部分

C．宪法规定了国家生活中的根本问题

D．宪法与普通法律是“国法”与“子法”的关系