Question

How many terms of the sequence -35 -28 -21.... should be taken so that their sum is zero?

Answer 1

The given sequence is an A.P.
where, first term (a) = -35
common difference (d) = 7
Let n be the required number of terms
Therefore,
0 = (n/2) [2a + (n-1)d ]
2a + (n-1)d = 0
2 (-35) + (n-1) 7 = 0
n-1 = (2 × 35)/7
n = 11