9th Class Mathematics Number System and its Operations Question Bank Number Systems

  • question_answer
    If\[x=\frac{1}{2-\sqrt{3}}\], find the value of\[{{x}^{3}}-2{{x}^{2}}-7x+10\].

    A)  \[14\]               

    B)         \[8\]                

    C)  \[4\]                

    D)         \[16\]               

    Correct Answer: B

    Solution :

    We have \[x=\frac{1}{2-\sqrt{3}}\] \[\Rightarrow \]\[x=\frac{1}{2-\sqrt{3}}\times \frac{2+\sqrt{3}}{2+\sqrt{3}}\] \[x-2=\sqrt{3}\] On squaring both sides \[{{x}^{2}}-4x+4-3\](or) \[{{x}^{2}}-4x+1=0\] Now on dividing \[{{x}^{3}}-2{{x}^{2}}-7x+10\,by\,{{x}^{2}}-4x+1,\] we get remainder 8. Hence, by using division algorithm we find \[{{x}^{3}}-2{{x}^{2}}-7x+10=({{x}^{2}}-4x+1)\text{(quotient)}+8\] On putting \[{{x}^{2}}-4x+1=0\]we get the value of \[{{x}^{3}}-2{{x}^{2}}-7x+10\,as\,8.\]


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