Question

If the 3rd term & 9th terms of an AP are 4 & -8 respectively, which term of the AP is zero

Answer 1

A9 = 0

a + 8d = 0

a = -8d ...... (1)

Now, to prove,

a29 = 2a19

a + 28d = 2(a + 18d)

a + 28d = 2a + 36d

-8d + 28d = -16d + 36d

20d = 20d