Math Problem Statement

Calculate two iterations of Newton's Method to approximate a zero of the function using the given initial guess: f(x) = cos(x), with an initial guess x₁ = 1.3. Round your answers to four decimal places.

Solution

The problem involves using Newton's Method to approximate a zero of the function f(x)=cos(x)f(x) = \cos(x), with an initial guess of x1=1.3x_1 = 1.3.

Newton's Method formula is: xn+1=xnf(xn)f(xn)x_{n+1} = x_n - \frac{f(x_n)}{f'(x_n)}

Steps to solve:

  1. Calculate f(x)f(x) and f(x)f'(x):

    • f(x)=cos(x)f(x) = \cos(x)
    • f(x)=sin(x)f'(x) = -\sin(x) (the derivative of cos(x)\cos(x))
  2. Start with the given initial guess x1=1.3x_1 = 1.3.

Let's go step by step through the first and second iterations.

Iteration 1 (for n=1n = 1):

  • x1=1.3x_1 = 1.3
  • f(x1)=cos(1.3)f(x_1) = \cos(1.3)
  • f(x1)=sin(1.3)f'(x_1) = -\sin(1.3)

Using a calculator:

  • cos(1.3)0.2675\cos(1.3) \approx 0.2675
  • sin(1.3)0.9636-\sin(1.3) \approx -0.9636

Now calculate the Newton's Method step: x2=x1f(x1)f(x1)=1.30.26750.96361.5776x_2 = x_1 - \frac{f(x_1)}{f'(x_1)} = 1.3 - \frac{0.2675}{-0.9636} \approx 1.5776

Iteration 2 (for n=2n = 2):

  • x21.5776x_2 \approx 1.5776
  • f(x2)=cos(1.5776)f(x_2) = \cos(1.5776)
  • f(x2)=sin(1.5776)f'(x_2) = -\sin(1.5776)

Using a calculator:

  • cos(1.5776)0.0002\cos(1.5776) \approx -0.0002
  • sin(1.5776)0.9999-\sin(1.5776) \approx -0.9999

Now calculate the next Newton's Method step: x3=x2f(x2)f(x2)=1.57760.00020.99991.5778x_3 = x_2 - \frac{f(x_2)}{f'(x_2)} = 1.5776 - \frac{-0.0002}{-0.9999} \approx 1.5778

Filling in the table:

nnxnx_nf(xn)f(x_n)f(xn)f'(x_n)f(xn)f(xn)\frac{f(x_n)}{f'(x_n)}xnf(xn)f(xn)x_n - \frac{f(x_n)}{f'(x_n)}
11.30000.2675-0.9636-0.27761.5776
21.5776-0.0002-0.99990.00021.5778

Would you like more details on how the values were calculated, or have any other questions? Here are some related questions:

  1. What is the significance of Newton's Method in solving equations?
  2. How does the choice of initial guess affect the convergence of Newton's Method?
  3. Can Newton's Method fail to converge, and if so, under what conditions?
  4. Why do we need to compute the derivative in Newton's Method?
  5. How accurate is Newton's Method compared to other root-finding algorithms?

Tip: Newton's Method converges faster when the initial guess is closer to the actual root.

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Math Problem Analysis

Mathematical Concepts

Calculus
Newton's Method
Root-finding

Formulas

Newton's Method: xₙ₊₁ = xₙ - f(xₙ) / f'(xₙ)

Theorems

Newton's Method for finding roots of a function

Suitable Grade Level

Undergraduate (Calculus I or II level)