Q. 65.0( 11 Votes )

Which term of an AP: 21, 42, 63, 84, … is 210?

Answer :

Given: AP: 21, 42, 63, 84, … is 210


To find: n for which an = 210.


Formula Used: nth term of an AP is:


an = a + (n - 1) d


Explanation:


Let nth term of the given AP be 210.


Here, first term, a = 21


and common difference,


d = 42 – 21 = 21 and an = 210


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


210 = 21 + (n - 1 )21


189 = (n - 1 )21


n - 1 = 9


n = 10


So, the 10th term of an AP is 210.


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