Find the sum of 10terms of an ap whose nth term is 1-4

Question

Find the sum of 10terms of an ap whose nth term is 1-4

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Liliana 1 month 2021-08-18T08:32:33+00:00 1 Answer 0 views 0

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  1. Charlotte
    0
    2021-08-18T08:33:49+00:00

    Answer:

    Step-by-step explanation:

    an=4n−1

    a1=a×1−1=3

    a2=4×2−1=7

    a3=4×3−1=11

    d=11−7=7−3=4  

    a=3

    n=20

    Sn=S20=n2[2a+(n−1)d]

    S20=202[2×3−(20−1)×4]

    S20=10[6+19×4]

    S20=10×[6+76]

    =10×82=820

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