过A直线斜率K：Y=KX+5
x^2+Y^2=98-Y^2
Y^2=(98-X^2)/2
-7<=Y<=7
PA^2=X^2+(Y-5)^2
=X^2+Y^2-10Y+25
=-Y^2-10Y+123
=-(y+5)^2+148
Y=-5,PAmax=2√37
y=7,PAmin=2
所以PA的最大2√37,最小2