Question

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

Answer 1

Solution: -8 = a + 8d
4 = a + 2d
Or, -8 – 4 = 6d
Or, -12 = 6d
Or, d = -2
Hence, a = -8 + 16 = 8
0 = 8 + -2(n-1)
Or, 8 = 2(n-1)
Or, n-1 = 4

Or, n = 5