10th Class Mathematics Polynomials Question Bank MCQs - Polynomials

  • question_answer
    The number of polynomials having zeroes as \[-2\] and 5 is:                                       (NCERT EXEMPLAR)

    A) 1

    B) 2

    C) 3

    D) more than 3

    Correct Answer: D

    Solution :

    [d] Let \[p(x)=a{{x}^{2}}+bx+c\] be the required polynomial whose zeroes are \[-2\]and 5.
    \[\therefore \]  Sum of zeroes \[=-\frac{b}{a}=-2+5\]
                            \[=\frac{3}{1}=-\frac{(-3)}{1}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,-\frac{b}{a}=-\frac{(-3)}{1}\]                      ….(1)
    and product of zeroes \[=\frac{c}{a}=-2\times 5=\frac{-10}{1}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\frac{c}{a}=\frac{-10}{1}\]             ….(2)
    From eqs. (1) and (2), \[a=1,\,b=-3\]and \[c=-10\]
    \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,\,p(x)={{x}^{2}}-3x-10\]
    But we know that, if we multiply/divide any polynomial by any arbitrary constant, then the zeroes of polynomial never change.
    \[\therefore \,\,\,\,\,\,p(x)=k{{x}^{2}}-3kx-10k,\]where k is a real number and \[p(x)=\frac{{{x}^{2}}}{k}-\frac{3}{k}x-\frac{10}{k},\]is a non-zero real number.
    Thus, the required number of polynomial is finite i.e., more than 3. Hence, out of given options, option [d] is correct.


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