10th Class Mathematics Pair of Linear Equations in Two Variables Question Bank MCQs - Pair of Linear Equations in Two Variables

  • question_answer
    The equations \[\text{3x}-\text{5y}=\text{7}\] and \[\text{9x}-\text{15y}=\text{21}\]have:

    A) a unique solution

    B) no solution

    C) infinitely many solutions 

    D) None of these

    Correct Answer: C

    Solution :

    [c] Given, \[3x-5y=7\] and \[9x-15y=21\]
    Here,   \[{{a}_{1}}=3,\,\,{{b}_{1}}=-5,\,\,{{c}_{1}}=7\]
    and   \[{{a}_{2}}=9,\,\,{{b}_{2}}=-15,\,\,{{c}_{2}}=21\]
    Now, \[\frac{{{a}_{1}}}{{{a}_{2}}}=\frac{3}{9}=\frac{1}{3},\,\,\,\frac{{{b}_{1}}}{{{b}_{2}}}=\frac{-5}{-15}=\frac{1}{3}\]
    and  \[\frac{{{c}_{1}}}{{{c}_{2}}}=\frac{7}{21}=\frac{1}{3}\,\,\,\,\,\,\Rightarrow \,\,\,\,\,\,\,\frac{{{a}_{1}}}{{{a}_{2}}}=\frac{{{b}_{1}}}{{{b}_{2}}}=\frac{{{c}_{1}}}{{{c}_{2}}}\]
    which shows that the given equations have infinitely many solutions.


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