JEE Advance - Mathematics (1994 - No. 28)
If $$In\left( {a + c} \right),In\left( {a - c} \right),In\left( {a - 2b + c} \right)$$ are in A.P., then
$$a,\,b,\,c$$ are in A.P.
$${a^2},\,{b^2},\,{c^2}$$ are in A.P.
$$a,\,b,\,c$$ are in G.P.
$$a,\,b,\,c$$ are in H.P.