If the 9th term of an A.P is five times the 5th term, find the relationship between a and d.
-
A.
2a + 2 = 0 -
B.
3a + 5d = 0 -
C.
a + 3d = 0 -
D.
a + 2d = 0
Correct Answer: Option C
Explanation
(T_{n} = a + (n – 1) d) (nth term of an AP).
(T_{9} = 5T_{5})
(a + 8d = 5(a + 4d) implies a + 8d = 5a + 20d)
(5a – a + 20d – 8d = 0 implies 4a + 12d = 0)
(a + 3d = 0)