Let three numbers in G.P. be a, ar, ar2Since the sum of the numbers is 21∴          a + ar + ar2 = 21...(i)Since the sum of the squares of the numbers is 189∴ ...(ii)Squaring both sides of (i), we get ...(iii)Dividing (iii) by (ii), we get              When r = 2, from (i), a = 3∴     Numbers are 3, 3(2), 3(2)2  or 3, 6, 12When     from (i),  a = 12∴ Numbers are 12,    or 12, 6, 3