10th Class Mathematics Polynomials Question Bank Polynomials

  • question_answer
    if a and b are the roots of the quadratic  equation \[{{x}^{2}}+px+12=0\]with the condition \[a-b=1,\]then the value of 'p' is _____.                                      

    A)  1                                

    B)  7                    

    C)         \[-7\]              

    D)         7 or \[-7\]                   

    Correct Answer: D

    Solution :

    Given equation is \[{{x}^{2}}+px+12=0\] Now, if a and b are its roots, then             Sum of roots,  \[a+b=-p\] and             Product of roots,  \[a\times b=12\]             Also,   \[a-b=1\]                      (Given)             We know that, \[{{(a-b)}^{2}}={{(a+b)}^{2}}-4ab\]             \[\Rightarrow \]            \[1={{p}^{2}}-4\times 12\,\,\,\,\,\,\Rightarrow \,\,\,\,1={{p}^{2}}-48\]             \[\Rightarrow \]            \[{{p}^{2}}=49\,\,\Rightarrow \,\,\,\,=\pm 7\]


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