Q.

If A, G and H are respectively the A.M., the G.M. and the H.M. between two positive numbers a and b, then the correct relation is

1 A=G2H  
2 A=GH2  
3 A2=GH  
4 G2=AH  

Ans.

(4)

For positive numbers a and b,

A=a+b2,  G=ab  and  H=2aba+b

Now,  AH=a+b2(2aba+b)=ab=G2

∴  The correct relation is, G2=AH