2a=4,a=2
x^2/4+y^2/b^2=1
1/4+(9/4)/b^2=1
b^2=3
C的方程:x^2/4+y^2/3=1
设:P(x,y)
则:|PQ|^2=x^2+(y-1/2)^2
=(4-4y^2/3)+(y-1/2)^2
=-y^2/3-y+17/4
=-(y+3/2)^2*1/3+5
所以,y=-3/2时,|PQ|^2有最大值=5
即:PQ最大值=√5
2a=4,a=2
x^2/4+y^2/b^2=1
1/4+(9/4)/b^2=1
b^2=3
C的方程:x^2/4+y^2/3=1
设:P(x,y)
则:|PQ|^2=x^2+(y-1/2)^2
=(4-4y^2/3)+(y-1/2)^2
=-y^2/3-y+17/4
=-(y+3/2)^2*1/3+5
所以,y=-3/2时,|PQ|^2有最大值=5
即:PQ最大值=√5