Question

How many terms of an ap 18 16 14 should be taken so that their sum is zero?

Answer 1

We know that sum = n/2(2a + (n-1) d)

                             0 = n/2(2 * 18 + (n - 1) * (-2))

                             0 = n/2(36-2n+2)

                             0 = 38n - 2n^2

                              2n^2 - 38n = 0

                              2n(n-19) = 0

                                 n - 19 = 0

                                 n = 19.


Hope this helps!