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\[-\text{ }5x+7y-2=0\]. The second equation can be

    A) \[10x+14y+4=0\]   

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

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

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

    Correct Answer: D

    Solution :

    Condition for dependent linear equations
    \[\frac{{{a}_{1}}}{{{a}_{2}}}=\frac{{{b}_{1}}}{{{b}_{2}}}=\frac{{{c}_{1}}}{{{c}_{2}}}=\frac{1}{k}\]        ...(i)
    Given equation of line is, \[-5x+7y-2=0\]
    Here,         \[{{a}_{1}}=-5,\,{{b}_{1}}=7,\,{{c}_{2}}=-2\]
    From Eq. (i), \[-\frac{5}{{{a}_{2}}}=\frac{7}{{{b}_{2}}}=-\frac{2}{{{c}_{2}}}=\frac{1}{k}\][say]
    \[\Rightarrow \,\,\,{{a}_{2}}=-5k,\ {{b}_{2}}=7k,\,{{c}_{2}}=-2k\]
    where, k is any arbitrary constant
    Putting k = 2, then \[{{a}_{2}}=-10\], \[{{b}_{2}}=14\]
    and  \[{{c}_{2}}=-4\]
    \[\therefore \] The required equation of line becomes
    \[{{a}_{2}}x+{{b}_{2}}y+{{c}_{2}}=0\]
    \[\Rightarrow \,\,\,\,-10x+14y-4=0\]
    \[\Rightarrow \,\,\,\,10x-14y+4=0\]


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