Math Problem Statement

use newton's method to estimate the two zeros of the function f(x) = x^4 - 2x - 2. Start with x0 = 1 for the zero on the right. then in each case, find x2.

Determine x2 when x0 = -1

x2= ____ type an integer or a simplified fraction

Then determine x2 when x0 = 1

x2 = ____ type an integer or a simplified fraction

Solution

To apply Newton's Method to estimate the zeros of the function f(x)=x42x2f(x) = x^4 - 2x - 2, we use the iterative formula:

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

Step 1: Find the derivative of f(x)f(x)

The function is f(x)=x42x2f(x) = x^4 - 2x - 2. The derivative is:

f(x)=4x32f'(x) = 4x^3 - 2

Step 2: Apply Newton's Method to estimate x2x_2 for x0=1x_0 = -1

  1. Starting with x0=1x_0 = -1:

    • f(1)=(1)42(1)2=1+22=1f(-1) = (-1)^4 - 2(-1) - 2 = 1 + 2 - 2 = 1
    • f(1)=4(1)32=42=6f'(-1) = 4(-1)^3 - 2 = -4 - 2 = -6
  2. Next, calculate x1x_1: x1=1f(1)f(1)=116=1+16=66+16=56x_1 = -1 - \frac{f(-1)}{f'(-1)} = -1 - \frac{1}{-6} = -1 + \frac{1}{6} = -\frac{6}{6} + \frac{1}{6} = -\frac{5}{6}

  3. Now, calculate x2x_2:

    • f(56)=(56)42(56)2f\left(-\frac{5}{6}\right) = \left(-\frac{5}{6}\right)^4 - 2\left(-\frac{5}{6}\right) - 2
    • f(56)=4(56)32f'\left(-\frac{5}{6}\right) = 4\left(-\frac{5}{6}\right)^3 - 2

We'll compute this exactly in a moment:

Step 3: Apply Newton's Method to estimate x2x_2 for x0=1x_0 = 1

  1. Starting with x0=1x_0 = 1:

    • f(1)=142(1)2=122=3f(1) = 1^4 - 2(1) - 2 = 1 - 2 - 2 = -3
    • f(1)=4(1)32=42=2f'(1) = 4(1)^3 - 2 = 4 - 2 = 2
  2. Next, calculate x1x_1: x1=1f(1)f(1)=132=1+32=52x_1 = 1 - \frac{f(1)}{f'(1)} = 1 - \frac{-3}{2} = 1 + \frac{3}{2} = \frac{5}{2}

  3. Now, calculate x2x_2:

    • f(52)=(52)42(52)2f\left(\frac{5}{2}\right) = \left(\frac{5}{2}\right)^4 - 2\left(\frac{5}{2}\right) - 2
    • f(52)=4(52)32f'\left(\frac{5}{2}\right) = 4\left(\frac{5}{2}\right)^3 - 2

Let me calculate both values and find the exact x2x_2 values for both cases. sympy import symbols, Rational, diff

Define the variable and function

x = symbols('x') f = x**4 - 2*x - 2 f_prime = diff(f, x)

Define the values for x0 = -1 and x0 = 1

x0_1 = -1 x0_2 = 1

Define the function evaluations

f_x0_1 = f.subs(x, x0_1) f_prime_x0_1 = f_prime.subs(x, x0_1)

f_x0_2 = f.subs(x, x0_2) f_prime_x0_2 = f_prime.subs(x, x0_2)

Calculate x1 for both cases

x1_1 = x0_1 - f_x0_1 / f_prime_x0_1 x1_2 = x0_2 - f_x0_2 / f_prime_x0_2

Calculate x2 for both cases

f_x1_1 = f.subs(x, x1_1) f_prime_x1_1 = f_prime.subs(x, x1_1)

f_x1_2 = f.subs(x, x1_2) f_prime_x1_2 = f_prime.subs(x, x1_2)

Calculate x2

x2_1 = x1_1 - f_x1_1 / f_prime_x1_1 x2_2 = x1_2 - f_x1_2 / f_prime_x1_2

x2_1.simplify(), x2_2.simplify()The values of x2x_2 for each starting point are as follows:

  • For x0=1x_0 = -1, x2=14891864x_2 = \frac{-1489}{1864}.
  • For x0=1x_0 = 1, x2=1907968x_2 = \frac{1907}{968}.

If you need more details or further calculations, feel free to ask!

Here are 5 questions to explore related concepts:

  1. How does the initial guess x0x_0 affect the convergence of Newton's method?
  2. How can Newton's method be applied to more complex functions, like those with multiple variables?
  3. What are the potential issues with Newton's method, such as divergence or slow convergence?
  4. How do you determine the number of iterations needed to achieve a desired level of accuracy in Newton's method?
  5. Can Newton's method be applied to functions that are not differentiable?

Tip: In Newton's method, if the derivative f(x)f'(x) is very small (close to zero), the method can behave unpredictably, so be careful with such values.

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Math Problem Analysis

Mathematical Concepts

Calculus
Numerical Methods
Root Finding
Newton's Method

Formulas

Newton's Method Formula: x_(n+1) = x_n - f(x_n) / f'(x_n)
Derivative of f(x) = x^4 - 2x - 2: f'(x) = 4x^3 - 2

Theorems

Newton's Method for Root Approximation

Suitable Grade Level

Grades 11-12 or College