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

  • question_answer
    One equation of a pair of dependent linear equations is \[-5x+7y=2\] The second equation can be:  (NCERT EXEMPLAR)

    A) \[10x+14y+4=0\]

    B) \[-10x-14y+4=0\]

    C) \[-10x+14y+4=0\]

    D) \[10x-14y=-4\]

    Correct Answer: D

    Solution :

    [d] Given equation of line is \[-5x+7y-2=0\]
    Here,       \[{{a}_{1}}=-5,\,\,{{b}_{1}}=7,\,\,{{c}_{1}}=-2\]
    Since, condition for dependent linear equation is          
    \[\frac{{{a}_{1}}}{{{a}_{2}}}=\frac{{{b}_{1}}}{{{b}_{2}}}=\frac{{{c}_{1}}}{{{c}_{2}}}=\frac{1}{k},\] where, k is any arbitrary constant
    \[\therefore \,\,\,\,\,\,\,\,\,\,\,-\frac{5}{{{a}_{2}}}=\frac{7}{{{b}_{2}}}=-\frac{2}{{{c}_{2}}}=\frac{1}{k}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,{{a}_{2}}=-5k,\,\,{{b}_{2}}=7k,\,\,{{c}_{2}}=-2k\]
    Substituting \[k=2,\] we get \[{{a}_{2}}=-10,\,\,{{b}_{2}}=14\]and \[{{c}_{2}}=-4\]
    \[\therefore \] The required equation of line becomes
                \[-10x+14y-4=0\]
    \[\Rightarrow \,\,\,\,10x-14y+4=0\]  or \[10x-14y=-4\]


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