Q1 of 180 Page 2

In an AP, if d = – 4, n = 7 and an = 4, then what is the value of a?

OR


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


4 = a + (7 – 1)(– 4)


4 = a – 24


a = 24 + 4 = 28


OR


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


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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