Q1 of 69 Page 78

Choose the correct alternative answer for each of the following sub questions.

In an A.P. first two terms are – 3, 4 then 21st term is . . .

Given: first term a = – 3


Second term t1 = 4


Common difference d = t1 – a = 4 – ( – 3) = 4 + 3 = 7


We need to find t21 where n = 21


Now, By using nth term of an A.P. formula


tn = a + (n – 1)d


where n = no. of terms


a = first term


d = common difference


tn = nth terms


Substituting all given value in the formulae we get,


⇒ t21 = – 3 + (21 – 1) × 7


⇒ t21 = – 3 + 20 × 7


⇒ t21 = – 3 + 140 = 137


Hence, correct answer is (C)

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