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In an increasing geometric series, the sum of the second and the sixth term is 2 5 2  and the product of the third and fifth term is 25. Then, the sum of 4th, 6th and 8th terms is equal to

Option 1 -

26

Option 2 -

35

Option 3 -

30

Option 4 -

32

0 2 Views | Posted a month ago
Asked by Shiksha User

  • 1 Answer

  • P

    Answered by

    Payal Gupta | Contributor-Level 10

    a month ago
    Correct Option - 2


    Detailed Solution:

    Let a, ar, ar2, . an increasing G.P then r > 1 & a > 0

    given : ar + ar5 = 252 .(i)

    and ar2ar4=25⇒a2r6=25⇒(ar3)2=25

    ⇒ar3=5.......(ii)

    From (i) and (ii), ar(1+r4)ar3=252×5

    ⇒2+2r4=5r2⇒2r4−5r2+2=0

    ⇒(2r2−1)(r2−2)=0

    ⇒r2=12,2∴r2=2⇒r=2

    ∴t4+t6+t8=5+10+20=35

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1In an increasing arithmetic progression a1, a2,....an if a5 = 2 and product of a1, a5 and a4 is greatest, then the value of dis equal to
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alok kumar singh

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Using (1)

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at  ( 8 5 ) , product attains maxima

-> d = 1.6

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alok kumar singh

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alok kumar singh

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