If 7 times the 7th term of an AP is equal to 11 times its 11th term, then its 18th term will be
Let a and d be first term and common difference respectively
According to the question,
7a7 = 11a11
As we know, nth term of an AP is
an = a + (n - 1)d
where a = first term
an is nth term
d is the common difference
we have
7(a + 6d) = 11(a + 10d)
7a + 42d = 11a + 110d
4a + 68d = 0
a + 17d = 0
a18 = 0
18th term of AP is 0