Q. 23.7( 3 Votes )

Mark the correct A. 2/5

B. 3/5

C. 2/5

D. none of these

Answer :

Given GP has first term unity


a1 = 1.


Hence the GP will become


1,r,r2,…


As given 4a2+5a3 is least


4r + 5r2 is least


We can say f(r) = 4r + 5r2


Now the given function will be least if df(r)/dr =0



8+10r=0


8=-10r


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