10th Class Mathematics Polynomials Question Bank MCQs - Polynomials

  • question_answer
    If the sum of the zeroes of the quadratic polynomial \[k{{x}^{2}}+2x+3k\] is equal to their product, then k equals:   (CBSE 2020)

    A) \[\frac{1}{3}\]

    B) \[-\frac{1}{3}\]

    C) \[\frac{2}{3}\]

    D) \[-\frac{2}{3}\]

    Correct Answer: D

    Solution :

    [d] Let \[f(x)=k{{x}^{2}}+2x+3k\]
    If \[\alpha \] and \[\beta \] are the zeroes of \[f(x)\]
    Then \[\alpha +\beta =-\frac{(2)}{k}\]
    and    \[\alpha \cdot \beta =\frac{3k}{k}=3\]
    According to question,
                \[\alpha +\beta =\alpha \beta \]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,-\frac{2}{k}=3\,\,\,\,\,\,\,\,\,\,\,\Rightarrow k=-\frac{2}{3}\]


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