9th Class Mathematics Polynomials Question Bank Polynomials

  • question_answer
    If \[(x+k)\] is a common factor of \[f(x)=({{x}^{2}}+px+q)\]and\[g(x)=({{x}^{2}}+lx+m),\]then the value of k is ____.

    A) \[l+p\]                          

    B) \[m-q\]  

    C)        \[\frac{l-p}{m-q}\]         

    D)        \[\frac{m-q}{l-p}\]         

    Correct Answer: D

    Solution :

    Since \[(x+k)\]is a common factor of \[f(x)={{x}^{2}}+px+q\]and \[g(x)={{x}^{2}}+lx+m\] Then, \[f(-k)=0\]and\[g(-k)=0\] \[\Rightarrow \]\[{{k}^{2}}-kp+q=0\]and \[{{k}^{2}}-kl+m=0\] \[\Rightarrow \]\[{{k}^{2}}=kp-q\]                                              ?(i) and \[{{k}^{2}}=kl-m\] From (i) and (ii), we have \[kp-q=kl-m\] \[\Rightarrow \]\[k=\frac{q-m}{p-l}\Rightarrow k=\frac{m-q}{l-p}\]


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