a,b,c,d are in increasing GP. AM between a and b is 6. AM between c and d is 54. Then AM between a and d is: (A)15 (B)48 (C)44 (D)42 Share with your friends Share 1 Neha Sethi answered this Let α be the first term and r be common ration of the given G.PGiven a,b,c,d are in increasing G.Pi.e., α,αr,αr2,αr3 are in increasing G.Pand a+b2=6 ⇒α+αr2=6⇒α(1+r)=12 ...(1)and c+d2=54⇒αr2+αr32=54⇒αr2(1+r)=108⇒r2×12=108 [using 1]⇒r2=9⇒r=±3When r=3 then (1) becomesα(1+3)=12⇒α=3When r=-3 then (1) becomesα(1-3)=12⇒α=-6So, A.M between a and d=a+d2=α+αr32=3+3332 or -6+(-6)-332=42 or 78Please recheck your options. 7 View Full Answer Tejas answered this In the soln.u can also take value of a as -6 but it wll not give the required ans available in options.so a=3 for options. 1