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]
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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
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