If an A.P., a G.P. and a H.P. have the same first term and same `(2n+1)` th term and their `(n+1)^n` terms are a,b,c respectively, then the radius of the circle. `x^2+y^2+2bx+2ky+ac=0` is

If the first and the (2n-1)^th term of an A.P,G.P anf H.P are equal and their nth term are a,b,c respectively,then

If first and (2n-1)^th terms of an AP, GP. and HP. are equal and their nth terms are a, b, c respectively, then

If the first and (2n-1)^(th) terms of an A.P,a G.P and an H.P of positive terms are equal and their (n+1)^(th) terms are a,b&c respectively then

If first and (2n-1)^(th) terms of A.P., G.P. and H.P. are equal and their nth terms are a,b,c respectively, then

If the first and (2n-1)^(th) terms of an A.P, a G.P and an H.P of positive terms are equal and their (n+1)^(th) terms are a, b & c respectively then

If the first and (2n + 1)th terms of an A.P. , G.P. and H.P. are equal and their (n + 1)th terms are a, b and c respectively, then

If the first & the (2n + 1)th terms of an A.P. , a G.P & an H.P. of positive terms are equal and their (n + 1)th terms are a, b & c respectively , then

An A.P. and a G.P. of positive terms have the same first term and the sum of their first, second and third terms are respectively, 1, 1/2 and 2. Show that the sum of their fourth terms is 19/2