10th Class Mathematics Polynomials Question Bank MCQs - Polynomials

  • question_answer
    If  the   zeroes   of  the   quadratic   polynomial \[{{x}^{2}}+(a+1)x+b\] are \[2\] and \[-3,\] then:   (NCERT EXEMPLAR)

    A) \[a=-7,\,\,b=-1\]

    B) \[a=5,\,\,b=-1\]

    C) \[a=2,\,b=-6\]   

    D) \[a=0,\,b=-6\]

    Correct Answer: D

    Solution :

    [d] Let \[p(x)={{x}^{2}}+(a+1)x+b\]
    Given that 2 and \[-3\]are the zeroes of the quadratic polynomial \[p(x)\].
    \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,p(2)=0\] and \[p(-3)=0\]
    Now,     \[p(2)=0\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{2}^{2}}+(a+1)\,(2)+b=0\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,2a+b=-6\]                                ….(1)
    Also,     \[p(-3)=0\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,{{(-3)}^{2}}+(a+1)\,(-3)+b=0\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,3a-b=6\]                             …..(2)
    On solving eqs. (1) and (2), we get
    \[a=0,\,\,b=-6\]


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