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Rajan@2021
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Find the A.P. whose nth term is 7-3n.Also find the 20th term

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One of the important question from the book -ML aggarwal( avichal publication)class 10th , chapter9, arithmetic progression ……..
This type of question has been asked in paper. so please solve it in detail.
Find the A.P. whose nth term is 7-3n.Also find the 20th term

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1 Answer

  1. Let first term of AP be, a

    Common difference be d

    According to question,

    nth term is  =>   73n=a+(n1)d

    =>  a+ndd=73n

    By comparing coefficents, we get
    a=4 &  d=3

    So, sum first 25 terms,

    2n[2a+(n1)d]

    =>  225[2×4+(251)(3)]

    =>  225[872]

    =>  400

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