9th Class Mathematics Number System and its Operations Question Bank Number System

  • question_answer
    If \[a=\frac{x}{x+y}\] and \[b=\frac{x}{x-y}\], then \[\frac{ab}{a+b}\] is equal to:

    A) \[\frac{xy}{{{x}^{2}}+{{y}^{2}}}\] 

    B)        \[\frac{{{x}^{2}}+{{y}^{2}}}{xy}\]

    C) \[\frac{x}{x+y}\]                      

    D) \[{{\left( \frac{y}{x+y} \right)}^{2}}\]

    E) None of these

    Correct Answer: A

    Solution :

    Explanation Option [a] is correct. \[\frac{ab}{a+b}=\frac{\frac{x}{(x+y)}\times \frac{y}{(x-y)}}{\frac{x}{(x+y)}+\frac{y}{(x-y)}}\] \[=\frac{xy}{{{x}^{2}}-xy+xy+{{y}^{2}}}=\frac{xy}{{{x}^{2}}+{{y}^{2}}}\]


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