This question is from NCERT Book class 10th Ch. no.5 Ex. 5.2 Q. 2 (ii). In this question you have to find the right option and support your answer by giving its solution. Answer the question with brief explanation.
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Choose the correct choice in the following and justify. (i) 30th term of the A.P: 10,7, 4, …, is (A) 97 (B) 77 (C) −77 (D) −87
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Solution:
It is given
A.P = 10, 7, 4, …
So, we can find,
1st term, a = 10
common diff., d = a2 − a1 = 7−10 = −3
For an A.P we use,
an = a +(n−1)d
Putting down the value:-
a30 = 10 + (30−1)(−3)
a30 = 10 + (29)(−3)
a30 = 10 − 87 = −77
So, the correct answer is option C.