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Rajan@2021
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Show that a1 ,a2 ,…,an form an AP where an =3+4n Also find the sum of the first 15 terms.

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Prove that a1 ,a2 ,…,an form an AP where an =3+4n Also find the sum of the first 15 terms of AP.

Sir please give me a detailed solution of this question as it is very important for examination

ML Aggarwal

Avichal Publication

Arithmetic Progression

Chapter 9 Question no 12

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1 Answer

  1. a1=3+4(1)=7
    a2=3+4(2)=11
    a2=3+4(3)=15

    d=a3a1=117=4

    Here a=7d=4 and n=15

    By usingSn=2n[2a+(n1)d] we have,

    S15=215[2×7+(151)4]

    =215(14+56)

    =215×70=525

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