Find the sum of the first 20 terms of the sequence 2,8,14,20

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Find the sum of the first 20 terms of the sequence 2,8,14,20

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Trung Dũng 5 years 2021-08-31T10:19:38+00:00 1 Answers 11 views 0

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  1. Orla
    0
    2021-08-31T10:20:40+00:00
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    Answer:

    S20=230

    Step-by-step explanation:

    2,8,14,20

    first determine whether it is arithmetic progression or geometric sequence.

    • for AP

    Common difference (d) = second term – first term

    D=T2-T1 D=T3-T2

    D=8-2 D=14-8

    D=6 D=6

    • Also try for GP

    COMMON RATIO= T2/T1

    r=T2/T1 r=T3/T2

    r=8/2 r=14/8

    r=4 r=7/4

    therefore, we can conclude that this is AP since we have the same common differences in the sequence

    Sn=n/2[2a+(n-1)].

    where,

    a=first term

    n=number of terms

    S20=20/2[2*2+(20-1)]

    S20=10(4+19)

    S20=10(23)

    S20=230

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Giải phương trình 1 ẩn: x + 2 - 2(x + 1) = -x . Hỏi x = ? ( )