Q10 of 47 Page 1

How many terms of the A.P. …. are needed to give their sum zero?

Given: First term = a = -6

Common difference = d = -11/2 – (-6)


⇒ d = 1/2


Sum of n terms = Sn = 0


We have to find n.


We know that Sum of n terms, Sn =


⇒ So, 0 =


⇒ n [-12 + 1/2(n – 1)] = 0


⇒ n [-24 + n – 1]/2 = 0


⇒ n [-25 + n] = 0


⇒ n = 0 (or) (-25 + n) = 0


⇒ n = 0 (or) n = 25


⇒ n = 0 cannot be admissible.


So, number of terms is 25.


Ans. 25 terms of the given A.P. are needed to give their sum zero.


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