Sequence And Series Question 20
Question: The harmonic mean of $ \frac{a}{1-ab} $ and $ \frac{a}{1+ab} $ is
[MP PET 1996; Pb. CET 2001]
Options:
A) $ \frac{a}{\sqrt{1-a^{2}b^{2}}} $
B) $ \frac{a}{1-a^{2}b^{2}} $
C) $ a $
D) $ \frac{1}{1-a^{2}b^{2}} $
Show Answer
Answer:
Correct Answer: C
Solution:
$ H.M.=\frac{2( \frac{a^{2}}{1-a^{2}b^{2}} )}{\frac{a}{1-ab}+\frac{a}{1+ab}}=\frac{2a^{2}}{2a}=a $ .
BETA
