Question

If the 3rd and the 9th terms of an AP are 4 and -8 respectively, which term of this AP is zero. Please help me guys.

Answer 1

Answer:

a3- 3rd term of AP

a9- 9th term if AP

a3 = a + 2d = 4 --------eq(1)

a9 = a + 8d = -8 --------eq(2)

eq(2) - eq(1) = 6d = -12

                       d = -2

therefore, eq(1)  gives,

          a + 2×-2 = 4       (d= -2)    

          a - 4 = 4

          a = 8

a=8, d= -2, an= 0

an= a + (n-1)d

8+(n-1)×-2 = 0

(n-1)×-2 = -8

n-1 = -8/-2 = 4

n=4+1 = 5

n=5

5th term of this AP is 0.

hope it helps