Sequence And Series Question 417
Question: The sum of the series 3.6 + 4.7 + 5.8 + ……upto (n - 2) terms
Options:
A) $ n^{3}+n^{2}+n+2 $
B) $ \frac{1}{6}(2n^{3}+12n^{2}+10,n-84) $
C) $ n^{3}+n^{2}+n $
D) None of these
Show Answer
Answer:
Correct Answer: B
Solution:
[b] $ S=3.6+4.7+….. $ up to $ n-2 $ terms $ =(1.4+2.5+3.6+4.7+………uptonterms)-14 $ $ =\Sigma n,(n+3)-14=\frac{1}{6}(2n^{3}+12n^{2}+10n)-14 $ $ =( \frac{2n^{3}+12n^{2}+10n-84}{6} ), $ where $ n=3,4,5…… $
BETA
