题目内容

已知动点P在椭圆
x2
25
+
y2
16
=1上,若A点坐标为(3,0),且|
AM
|=1,且
PM
AM
=0,则|
PM
|的最小值是(  )
A.
2
B.
3
C.2D.3
PM
AM
=0,∴
PM
AM
=0,
∴|
PM
|2=|
AP
|2-|
AM
|2
∵|
AM
|=1,∴|
AM
|2=1,
∴|
PM
|2=|
AP
|2-|
AM
|2=|
AP
|2-1,
∵|
AM
|=1,
∴点M的轨迹为以为以点A为圆心,1为半径的圆,
∵|
PM
|2=|
AP
|2-1,|
AP
|越小,|
PM
|越小,
结合图形知,当P点为椭圆的右顶点时,
|
AP
|取最小值a-c=5-3=2,
∴|
PM
|最小值是
4-1
=
3

故选:B.
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