The value of k for which the circles x^2+y^2=1 and x^2+y^2-4kx+8=0 have only two common tangents is
(a) (-9/4,9/4) (b) k<-9/4 & k>9/4 (c)none of these
The value of k for which the circles x^2+y^2=1 and x^2+y^2-4kx+8=0 have only two common tangents is
(a) (-9/4,9/4) (b) k<-9/4 & k>9/4 (c)none of these