JCECE Engineering JCECE Engineering Solved Paper-2011

  • question_answer
    The equation \[{{x}^{3}}-3x+4=0\] has only one real root. What is its first approximate value as obtained by the method of false position in\[(-3,\,\,-2)\]?

    A) \[-2.125\]                           

    B) \[2.125\]

    C) \[-2.812\]                           

    D) \[2.812\]

    Correct Answer: A

    Solution :

    We have,\[{{x}_{2}}={{x}_{0}}-\frac{{{x}_{1}}-{{x}_{0}}}{f({{x}_{1}})-f({{x}_{0}})}\] Here,\[{{x}_{0}}=-3,\,\,{{x}_{1}}=-2,\,\,f(x)={{x}^{3}}-3x+4\] \[\therefore \]  \[f({{x}_{0}})=-27+9+4=-14\]                 \[f({{x}_{1}})=-8+6+4=2\] So,          \[{{x}_{2}}=-3-\frac{1}{16}\times (-14)\] \[=-3+\frac{7}{8}=-\frac{17}{8}=-2.125\]


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