Q. 83.7( 10 Votes )

If the 3rd and the 9th terms of an AP are 4 and -8 respectively, which term of this AP is zero?

Answer :

Given

an = 0, n = ?


3rd term = 4


a + (3-1)d = 4 1


9th term = 73


a + (9-1)d = -8 2


By subtracting the both equations we will get ‘d’


(a +2d) – (a+8d) = 4 – (-8)


-6d = 12


d = -2


By substituting “d” in equation 1


a +2d = 4


a + (-2)2 = 4


a = 8


an = a+(n-1)d


0 = 8+(n-1)(-2)


-8 = (n-1)(-2)


4 = n-1


n = 5


0 is the 5th term in the series.


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