The iterative formula to find the root of the equation f(x) = x3 - 5x + 7 = 0 by the Newton Raphson method is ______.

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BDL MT Electrical 17 April 2022 Official Paper
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  1. \({x_{k + 1}}\, = \,\frac{{x_k^3\, - \,5x}}{{3x_k^2 + 7}}\)
  2. \({x_{k + 1}}\, = \,\frac{{2x_k^3\, + \,5x}}{{3x_k^2 + 7}}\)
  3. \({x_{k + 1}}\, = \,\frac{{2x_k^3\, - \,7}}{{3x_k^2 - 5}}\)
  4. \({x_{k + 1}}\, = \,\frac{{x_k^3\, + \,5x - 7}}{{3x_k^2 + 5}}\)

Answer (Detailed Solution Below)

Option 3 : \({x_{k + 1}}\, = \,\frac{{2x_k^3\, - \,7}}{{3x_k^2 - 5}}\)
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Detailed Solution

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Concept:

Newton Raphson method:

The iteration formula is  \(x_{n+1} = x_n - \frac {f(x)}{f'(x)} \)

Calculation:

Given

\(f(x)=x^3 -5x+7\)

\(x_{n+1} = x_n - \frac {f(x)}{f'(x)} \)

\(f'(x) = 3x^2 -5\)

\(x_{k+1} = x_k- (\frac{x_k^3-5x+7}{3x_k^2 -5})\) \(x_{k+1} =\frac{3x_k^3 -5x_k-x_k^3+5x_k-7}{3x_k^2-5}\) ⇒ \(x_{k+1} = \frac{2x_k^3-7}{3x_k^2-5}\)

 

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