The harmonic mean of \[\frac{a}{1-ab}\] and \[\frac{a}{1+ab}\] is [MP PET 1996; Pb. CET 2001]

\[\frac{1}{1-{{a}^{2}}{{b}^{2}}}\]

\[\frac{a}{\sqrt{1-{{a}^{2}}{{b}^{2}}}}\]

\[\frac{a}{1-{{a}^{2}}{{b}^{2}}}\]

The harmonic mean of \[\frac{a}{1-ab}\] and \[\frac{a}{1+ab}\] is [MP

1.	The harmonic mean of \[\frac{a}{1-ab}\] and \[\frac{a}{1+ab}\] is [MP PET 1996; Pb. CET 2001]
A.	\[\frac{a}{\sqrt{1-{{a}^{2}}{{b}^{2}}}}\]
B.	\[\frac{a}{1-{{a}^{2}}{{b}^{2}}}\]
C.	\[a\]
D.	\[\frac{1}{1-{{a}^{2}}{{b}^{2}}}\]
Answer» D. \[\frac{1}{1-{{a}^{2}}{{b}^{2}}}\]

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The harmonic mean of \[\frac{a}{1-ab}\] and \[\frac{a}{1+ab}\] is [MP PET 1996; Pb. CET 2001]

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