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Deepak Bora
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If the 3rd and 9th terms of an A.P. are 4 and − 8 respectively. Which term in this A.P. is zero.

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The question is given from NCERT Book of class 10th Ch. no. 5 Ex. 5.2 Q. 8. In the following question you have to find which term in this series will be zero if 3rd term is 4 & 9th term is -8.

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1 Answer

  1. Solution: 

    3rd term, a3 = 12

    50th term, a50 = 106

    We know,

    an = a+(n−1)d

    a3 = a+(3−1)d

    12 = a + 2d       ……………………………. (i)

    Like this,

    a50 a + (50−1)d

    106 = a + 49d     …………………………. (ii)

    By subtracting  (i) from (ii),

    94 = 47d

    d = 2

    From equation (i),

    12 = a + 2(2)

    a = 12 − 4 = 8

    a29 = a + (29−1) d

    a29 = 8 + (28)2

    a29 = 8 + 56 = 64

    The 29th term of the give A.P is 64.

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