已知圆(x+2)+(y-4)=19关于直线2ax-by+8=0(a,b>0)对称,则8/a+2/b

圆(x+2)+(y-4)=19关于直线2ax-by+8=0(a,b>0)对称,则8/a+2/b的最小值为?
圆心为 (-2,4)
代入 2ax-by+8=0
-4a-4b = -8
a+b = 2
8/a+2/b
=(8/a+2/b)*(a+b)/2
=(4+4b/a+a/b+1)
=5+4b/a+a/b
>=5+2根号4
=9