Question

Iii. if the 3rd term and 9th term of an a.p series are 4 and -8
respectively. which term of this a.p is zero? [3]

Answer 1

Step-by-step explanation:

3rd term = 4 9th term = -8

a + 2d = 4 (eq1) a + 7d = -8 (eq2)

from eq (1) & (2)

a + 2d = 4

a + 7d = -8

- - +

------------------

-5d = 12

-d = 12/5

d = -(12/5)

d=-(12/5) in eq 1

a + 2d = 4

a + 2 (-12/5) = 4

a - 24/5 = 4

a = 4 + 24/5

a = 20 + 24/5

a = 44/5

an = a1 + (n-1)d

an = 0 , a1 = 44/5, d=(-12/5)

0 = 44/5 + (n-1)(-12/5)

0=44/5 -12/5n + 12/5

0= 56/5 - 12/5n

12/5n = 56/5

n = (56/5)/(12/5)

n=56/12

n = 4.66

Therefore zero will not come in this ap