This is the Important question based on Arithmetic progression Chapter of R.S Aggarwal book for ICSE & CBSE

Board.

In this question you have to find the number of term on which the AP becomes zero.

This is the Question Number 10 Of Exercise 11 D of RS Aggarwal Solution.

# Which term of the AP 21,18,15,….is zero?

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The given is in A.P.

⇔ 21,18,15

a=21

a+d=18

d = -3

⇒a(nth term)= a+(n-1)d

⇒0=a+(n-1)d

⇒0=21+[n-1](-3)

⇒n-1 = -21/-3

⇒n-1 = 7

⇒n =8.