Let {an}n=0 be a sequence such that a0 = a1 = 0 and an+2 = 3an+1 – 2an + 1, n0. Then a25a232a25a222a23a24+4a22a24 is equal to

Option 1 -

483   

Option 2 -

528

Option 3 -

575

Option 4 -

624

0 4 Views | Posted 3 months ago
Asked by Shiksha User

  • 1 Answer

  • P

    Answered by

    Payal Gupta | Contributor-Level 10

    3 months ago
    Correct Option - 2


    Detailed Solution:

    a0 = 0, a1 = 0

    an+2 = 3an+1 – 2an + 1

    a25 a23 – 2a25a22 – a23a24 + 4a22a24 =?

    a2 = 3a1 – 2a0 + 1

    a3 = 3a2 – 2a1 + 1

    a4 = 3a3 – 2a2 + 1

    a5 = 3a4 – 2a3 + 1

    an+2  = 3an+1 – 2an + 1

    ( + ) ( a 2 + a 3 + a 4 + . . . . + a n + 1 + a n + 2 )                

    ⇒ an+2 = 2 (a2 + a3 + …. + an + an+1) –2 (a1 + a2 + ….+ an) + n + 1

    an+2 = 2an+1 + n + 1

    a25 a23 -2a25 a22 -a23 a24 + 4a22 a24

    = a25 (a23 – 2a22) -2a24 (a23 – 2a22)

    As an+2 = 2an+1 + n + 1

    ⇒ an+2 – 2an+1 = n + 1

    ⇒ an+1 -2an = n

    ⇒ 24 × 22 = 528

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