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Mathematics

a1a1+b1\dfrac{a^{-1}}{a^{-1} + b^{-1}} is equal to :

  1. ba+b\dfrac{b}{a + b}

  2. a+ba\dfrac{a + b}{a}

  3. aa+b\dfrac{a}{a + b}

  4. a(a + b)

Indices

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Answer

Simplifying the expression :

a1a1+b1=1a1a+1b=1ab+aab=aba(b+a)=ba+b.\Rightarrow \dfrac{a^{-1}}{a^{-1} + b^{-1}} = \dfrac{\dfrac{1}{a}}{\dfrac{1}{a} + \dfrac{1}{b}} \\[1em] = \dfrac{\dfrac{1}{a}}{\dfrac{b + a}{ab}} \\[1em] = \dfrac{ab}{a(b + a)} \\[1em] = \dfrac{b}{a + b}.

Hence, Option 1 is the correct option.

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