Math Problem Statement

An approximate solution to x^3 + 4x^2 + 6 = 0 can be found using this iterative formula: x_{n+1} = -4 - 6/x_n^2. Use this formula to work out an approximate solution to the equation, starting with x_1 = -2.5. Give your answer to 2 d.p.

Solution

The image provides the following iterative formula to solve for xx:

xn+1=46xn2x_{n+1} = -4 - \frac{6}{x_n^2}

The initial approximation for xx is given as x1=2.5x_1 = -2.5. We are tasked with using this formula to find an approximate solution to the equation x3+4x2+6=0x^3 + 4x^2 + 6 = 0, and give the answer to 2 decimal places.

Step-by-step Calculation:

  1. Iteration 1: Using x1=2.5x_1 = -2.5: x2=46(2.5)2x_2 = -4 - \frac{6}{(-2.5)^2} x2=466.25x_2 = -4 - \frac{6}{6.25} x2=40.96=4.96x_2 = -4 - 0.96 = -4.96

  2. Iteration 2: Using x2=4.96x_2 = -4.96: x3=46(4.96)2x_3 = -4 - \frac{6}{(-4.96)^2} x3=4624.60x_3 = -4 - \frac{6}{24.60} x3=40.24=4.24x_3 = -4 - 0.24 = -4.24

  3. Iteration 3: Using x3=4.24x_3 = -4.24: x4=46(4.24)2x_4 = -4 - \frac{6}{(-4.24)^2} x4=4617.98x_4 = -4 - \frac{6}{17.98} x4=40.33=4.33x_4 = -4 - 0.33 = -4.33

Thus, after a few iterations, the value of xx seems to stabilize around 4.33-4.33. Therefore, the approximate solution to the equation is:

x4.33x \approx -4.33

Would you like any further details on this process or more iterations? Let me know!

Here are 5 related questions:

  1. How does the iterative method converge to a solution?
  2. What happens if you start with a different initial guess for x1x_1?
  3. How can we verify the accuracy of this approximate solution?
  4. What are some alternative methods for solving cubic equations like this one?
  5. Why does this specific iterative method work for this equation?

Tip: Iterative methods often require a good initial guess to converge faster; choosing a poor initial guess can lead to slower convergence or divergence.

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Math Problem Analysis

Mathematical Concepts

Algebra
Cubic Equations
Iterative Methods
Numerical Approximation

Formulas

x_{n+1} = -4 - 6/x_n^2

Theorems

Iterative Convergence Theorem

Suitable Grade Level

Grades 10-12