10th Class Mathematics Polynomials Question Bank Polynomials

  • question_answer
    Obtain all the zeroes of the polynomial \[f(x)=3{{x}^{4}}+6{{x}^{3}}-2{{x}^{2}}-10x-5,\]if two of its zeros are \[\sqrt{\frac{5}{3}}\] and \[-\sqrt{\frac{5}{3}}\].

    A)  \[1,-1\]                       

    B)  \[1,\,\,1\]                     

    C)         \[-1,-1\]          

    D)        \[1,0\]        

    Correct Answer: C

    Solution :

    \[\sqrt{\frac{5}{3}}\] and \[-\sqrt{\frac{5}{3}}\]  are the zeroes of polynomial \[f(x)\] \[\therefore \]   \[\left( x-\sqrt{\frac{5}{3}} \right),\,\left( x+\sqrt{\frac{5}{3}} \right)\] are factors of .i.e.,     \[\left( {{x}^{2}}-\frac{5}{3} \right)\] exactly divides f(x).   Now, \[3{{x}^{4}}+6{{x}^{3}}-2{{x}^{2}}-10x-5\] \[=\left( {{x}^{2}}-\frac{5}{3} \right)\,(3{{x}^{2}}+6x+3)=3\left( {{x}^{2}}-\frac{5}{3} \right){{(x+1)}^{2}}\]         For zeroes of polynomial f(x), \[f(x)=0\] \[\Rightarrow \] \[3\left( {{x}^{2}}-\frac{5}{3} \right){{(x+1)}^{2}}=0\] \[\Rightarrow \] \[x=\sqrt{\frac{5}{3}},\] \[-\sqrt{\frac{5}{3}},-1,-1\]


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