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