Question

How many terms in ap 18 16 14 must be taken so that their sum is zero?

Answer 1

The given AP is 18, 16, 14...
here, first term, a= 18
common difference, d = 16-18 = -2
Now, The number of terms = n
Sum of n term = 0 (given)
So, Sn = n/2 [2a+(n-1)d]
=> 0 = n/2 [ 2×18 + (n-1) × (-2)
=> 0 = n/2 × 2 (18-n+1]
=> 0 = n (19-n)
=> 19 - n = 0
=> n = 19

Therefore, 19 terms must be taken in the given AP so that their sum is 0.