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Rajan@2021
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If an = 3 – 4n, show that a1 , a2 , a3 …… form an A.P. Also find S20 ​ .

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It is given that an = 3 – 4n, prove that a1 , a2 , a3 …… form an A.P. Also find S20.

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 13

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  1. an=34n

    a1=34(1)=1

    a2=34(2)=5

    a3=34(3)=9

    a3a2=a2a1=4

    as it should shows constant common difference

     It is an AP with a=1 & d=4

    S20=220[2(1)+(201)(4)]

    S20=10[276]

    S20=780.

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