Q22 of 38 Page 5

If 7 times the 7th term of an AP is equal to 11 times its 11th term, then find the value of 18th term.

Given: 7a7 = 11a11


To find: a18


Formula Used:


nth term of an AP is:


an = a + (n - 1) d


Where an is the last term.


n = no of terms


a = first term


d = common difference


Explanation:


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


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


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