in an arithmetic progression if an =2n+1 then find the sum of first 20terms​

in an arithmetic progression if an =2n+1 then find the sum of first 20terms​

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  1. Answer:

    an =2n+1 S20=?

    Step-by-step explanation:

    let n=1

    a1=2×1+1

    a=2+1

    =3

    let n=2

    a2=2×2+1

    a2=4+1

    a2=5

    d=a2-a

    d=5-3

    d=2

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

    S20=20/2(2×3+19×2)

    S20=10(6+38)

    S20=10×44

    S20=440.

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