Finding the Iterative Function to Solve x3+x-1000=0

In summary, the conversation discusses the use of iterative methods to find the approximate root of an equation in a specific range. The iterative procedure involves calculating the next approximation using a function of the previous approximation, and it can converge when the derivative is less than 1. Suggestions for suitable iterative functions are given, with one being found to work effectively. The conversation also hints at another method that does not involve using cubic root in the iteration process.
  • #1
bb.minhtri
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Homework Statement



The iterative method is used to find the approximate root of the equation x3 + x - 1000 = 0 in [9, 10]. What is the suitable iterative function?

Homework Equations


The Attempt at a Solution


How to find the iterative function and is there any conditions for one?
Thanks for helps.
 
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  • #2
The iterative procedure is to calculate the next approximation of x from a function of the previous approximation: xi+1=f(xi). The iterative process can converge in a range of x where the derivative |df/dx |<1.

You can try the ways: x=1000-x3 or x=(1000-x)^1/3.
Which one works? And you can find other iterative functions for this equation. ehild
 
Last edited:
  • #3
ehild said:
The iterative procedure is to calculate the next approximation of x from a function of the previous approximation: xi+1=f(xi). The iterative process can converge in a range of x where the derivative |df/dx |<1.

You can try the ways: x=1000-x3 or x=(1000-x)^1/3.
Which one works? And you can find other iterative functions for this equation.

The second one works ^^ Thank you very much. Your explanation is very clear:D
 
  • #4
Using cubic root in an iteration process is not too nice. You can find an other method without that. Hint: write x^3-1000 in the form (x-10)(x^2+10x+100), and isolate x from the x-10 factor.

ehild
 

1. How do I find the iterative function to solve x3+x-1000=0?

To find the iterative function, we can use the Newton-Raphson method. This method involves repeatedly plugging in initial guesses for the root of the function and using the derivative of the function to refine the guess until we get a more accurate approximation.

2. What is the Newton-Raphson method?

The Newton-Raphson method is an iterative numerical method used to find the roots of a function. It involves using initial guesses and the derivative of the function to refine the guess until a satisfactory approximation for the root is found.

3. How do I know if my initial guess is close enough to the root?

You can use the error formula to determine the error between the actual root and your approximation. If the error is small enough, then your initial guess is close enough to the root and you can stop iterating.

4. Can I use any initial guess for the Newton-Raphson method?

Yes, you can use any initial guess for the Newton-Raphson method. However, choosing a good initial guess can help speed up the convergence of the method.

5. How accurate is the Newton-Raphson method?

The accuracy of the Newton-Raphson method depends on the initial guess and the function itself. In general, the method can provide very accurate approximations for the root of a function.

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