. In an AP if a = 1, aₙ= 20 and Sₙ = 399, then n is​

Question

. In an AP if a = 1, aₙ= 20 and Sₙ = 399, then n is​

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2 months 2021-08-13T13:59:57+00:00 2 Answers 0 views 0

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    0
    2021-08-13T14:01:43+00:00

    Step-by-step explanation:

    399 is the answer

    is it right

    0
    2021-08-13T14:01:44+00:00

    Answer:

    a= 1

    an =20

    sn=399

    SN= 1/2 (2a+(n-1)d

    so,

    sn=1/2 (2a+an)

    399=1/2 (2 n+20)

    …….

    solve yourself

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