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Math Lesson 9.4.4 - Recursive Iteration and Iteration Machines

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Welcome to our Math lesson on Recursive Iteration and Iteration Machines, this is the fourth lesson of our suite of math lessons covering the topic of Iterative Methods for Solving Equations, you can find links to the other lessons within this tutorial and access additional Math learning resources below this lesson.

Recursive Iteration. Iteration Machines

Sometimes, you will be given a formula to use in questions involving iteration. Such a formula - known as the "iteration machine" - is applied a number of times for variables unit until you obtain two same results in a row after rounding it to the desired number of decimal places. According to this procedure, if xn + 1 = xn when the result is rounded at the desired number of decimal places, then this result represents the root of the original equation. This method is known as the recursive iteration.

The general procedure used in iteration machines is as follows:

Math Tutorials: Iterative Methods for Solving Equations Example

Let's clarify this procedure through an example.

Example 6

Using the iteration machine, find a solution for the equation

x3 - 5x + 3 = 0

to one decimal place, by starting from x0 = 0

Solution 6

First, let's isolate x by finding a suitable transformation of the original equation. We will stop after obtaining two same results after rounding. Thus, we have:

x3 - 5x + 3 = 0
x3 = 5x - 3
x = 5x - 3

Now, we have to use the formula

xn + 1 = 5xn - 3

to calculate the value of x rounded to one decimal place. Thus, for x0 = 0, we have

x1 = 5x0 - 3
= 5 ∙ 0 - 3
= - 3
= - 1.4422
≈ - 1.4

For x1 = - 1.4422, we have

x2 = 5x1 - 3
= 5 ∙ ( - 1.4422) - 3
= - 10.2112..
= - 2.16949
≈ - 2.2

For x2 = - 2.16949, we have

x3 = 5x2 - 3
= 5 ∙ ( - 2.16949) - 3
= - 13.84749
= - 2.401359
≈ - 2.4

For x3 = - 2.401359, we have

x4 = 5x3 - 3
= 5 ∙ ( - 2.401359) - 3
= - 15.00679
= - 2.46658
≈ - 2.5

For x4 = - 2.46658, we have

x5 = 5x4 - 3
= 5 ∙ ( - 2.46658) - 3
= - 15.3329
= - 2.48432
≈ - 2.5

Thus, since we obtained the same result (x = - 2.5) in the last two steps after rounding them to one decimal place, we have x = - 2.5 as a solution for our original equation.

More Iterative Methods for Solving Equations Lessons and Learning Resources

Equations Learning Material
Tutorial IDMath Tutorial TitleTutorialVideo
Tutorial
Revision
Notes
Revision
Questions
9.4Iterative Methods for Solving Equations
Lesson IDMath Lesson TitleLessonVideo
Lesson
9.4.1Iterative Methods for Solving Equations
9.4.2Applications of Iterative Methods
9.4.3Exercises involving Iteration
9.4.4Recursive Iteration and Iteration Machines

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