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

  • question_answer
    The value of c for which the pair of equations \[cx-y=2\]and \[\text{6x}-\text{2y}=\text{3}\] will have infinitely many solutions is:                                                                                                                     (NCERT EXEMPLAR)

    A) \[3\]

    B) \[-3\]

    C) \[-12\]

    D) no value

    Correct Answer: D

    Solution :

    [d] The given equations of lines are                  
    \[cx-y=2\] and \[6x-2y=3\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,cx-y-2=0\]and \[6x-2y-3=0\]
    Here, \[{{a}_{1}}=c,\,{{b}_{1}}=-1,\,\,{{c}_{1}}=-2\]
    and   \[{{a}_{2}}=6,\,\,{{b}_{2}}=-2,{{c}_{2}}=-3\]
    Since, condition for infinitely many solutions is      
    \[\frac{{{a}_{1}}}{{{a}_{2}}}=\frac{{{b}_{1}}}{{{b}_{2}}}=\frac{{{c}_{1}}}{{{c}_{2}}}\Rightarrow \frac{c}{6}=\frac{-1}{-2}\] and \[\frac{c}{6}=\frac{-2}{-3}\]
                \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,c=3\] and \[c=4\]
    Since, c has different values.                              
    So, there exists no value of c for which given equations have infinitely many solutions.


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