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 k for which the system of linear equations \[x+2y=3\], \[5x+ky+7=0\] is inconsistent is

    A) \[-\frac{14}{3}\]

    B) \[\frac{2}{5}\]

    C) 5

    D) 10

    Correct Answer: D

    Solution :

    The condition that system of linear equations \[{{a}_{1}}x+{{b}_{1}}y+{{c}_{1}}=0\] and \[{{a}_{2}}x+{{b}_{2}}y+{{c}_{2}}=0\] is inconsistent, if
    \[\frac{{{a}_{1}}}{{{a}_{2}}}=\frac{{{b}_{1}}}{{{b}_{2}}}\ne \frac{{{c}_{1}}}{{{c}_{2}}}\]                                        ...(i)
    Given system of linear equations are
    \[x+2y=3\] or \[x+2y-3=0\]
    and \[5x+ky+7=0\]
    Here, \[{{a}_{1}}=1,\,{{b}_{1}}=2,\,{{c}_{1}}=-3\]
    and \[{{a}_{2}}=5,\,{{b}_{2}}=k,\,{{c}_{2}}=7\]
    From Eq. (i), we get
    \[\frac{1}{5}=\frac{2}{k}\ne -\frac{3}{7}\]
    Taking 1st and Und terms
    \[\frac{1}{5}=\frac{2}{k}\Rightarrow k=10\]


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