Question
If the 7th and 13th terms of an AP are 34 and 64, then its 18th term is ___.
Answer: Option C
:
C
The nth term of an AP of first term a and common difference d is
an=a+(n−1)d.⇒a7=a+6d=34−−−(1)a13=a+12d=64−−−(2)(2)−(1)⇒6d=30⇒d=5Substituting d = 5 in (1), we geta=4.∴a18=a+17d=4+(17)5=89
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:
C
The nth term of an AP of first term a and common difference d is
an=a+(n−1)d.⇒a7=a+6d=34−−−(1)a13=a+12d=64−−−(2)(2)−(1)⇒6d=30⇒d=5Substituting d = 5 in (1), we geta=4.∴a18=a+17d=4+(17)5=89
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