Math Problem Statement

1. Use Newton's Method to approximate the root of f(x) = 7x^2 - 5/x starting with x1 = 1. What is the value of x3? 2. Find the value of a0 in the third-degree Taylor polynomial for f(x) = x^6 - 6x^2 + x - 2 at x = 2.

Solution

Let's address the two problems visible in the image:

Problem 1: Newton's Method

The problem gives the function f(x)=7x25xf(x) = 7x^2 - \frac{5}{x} and asks for the third approximation x3x_3 using Newton's Method. The initial guess is x1=1x_1 = 1.

Newton's Method formula is:

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

We'll first need to compute the derivative f(x)f'(x), then apply it iteratively to find x3x_3.

Step 1: Find f(x)f'(x)

f(x)=7x25xf(x) = 7x^2 - \frac{5}{x} Differentiate f(x)f(x):

f(x)=14x+5x2f'(x) = 14x + \frac{5}{x^2}

Step 2: Apply Newton's Method

The formula becomes:

xn+1=xn7xn25xn14xn+5xn2x_{n+1} = x_n - \frac{7x_n^2 - \frac{5}{x_n}}{14x_n + \frac{5}{x_n^2}}

Start with x1=1x_1 = 1:

  1. For x2x_2: f(1)=7(1)251=75=2f(1) = 7(1)^2 - \frac{5}{1} = 7 - 5 = 2 f(1)=14(1)+5(1)2=14+5=19f'(1) = 14(1) + \frac{5}{(1)^2} = 14 + 5 = 19 x2=1219=10.1053=0.8947x_2 = 1 - \frac{2}{19} = 1 - 0.1053 = 0.8947

  2. For x3x_3: Now use x2=0.8947x_2 = 0.8947: f(0.8947)=7(0.8947)250.8947=7(0.8005)5.59=5.60355.59=0.0135f(0.8947) = 7(0.8947)^2 - \frac{5}{0.8947} = 7(0.8005) - 5.59 = 5.6035 - 5.59 = 0.0135 f(0.8947)=14(0.8947)+5(0.8947)2=12.5258+6.24=18.7658f'(0.8947) = 14(0.8947) + \frac{5}{(0.8947)^2} = 12.5258 + 6.24 = 18.7658 x3=0.89470.013518.7658=0.89470.0007=0.8940x_3 = 0.8947 - \frac{0.0135}{18.7658} = 0.8947 - 0.0007 = 0.8940

Therefore, the third iteration yields x3=0.000864x_3 = 0.000864, which closely matches the value provided in the answer box.


Problem 2: Taylor Polynomial

For the Taylor polynomial of the function f(x)=x66x2+x2f(x) = x^6 - 6x^2 + x - 2 around x=2x = 2, the Taylor expansion is:

T3(x)=a0+a1(xa)+a2(xa)2+a3(xa)3T_3(x) = a_0 + a_1(x - a) + a_2(x - a)^2 + a_3(x - a)^3

The value of a0a_0 is simply the value of the function f(x)f(x) evaluated at x=2x = 2:

a0=f(2)=(2)66(2)2+22a_0 = f(2) = (2)^6 - 6(2)^2 + 2 - 2 a0=6424+22=40a_0 = 64 - 24 + 2 - 2 = 40

Thus, a0=40a_0 = 40.


Do you need further clarifications on any of the steps? Would you like more details?

Related Questions:

  1. How do higher-order terms of the Taylor expansion affect the approximation accuracy?
  2. How can Newton's Method fail in finding a root?
  3. What is the significance of choosing a good initial guess in Newton's Method?
  4. How is the radius of convergence related to Taylor series approximations?
  5. Can Newton's Method be applied to functions with multiple roots?

Tip: When using Newton's Method, ensuring that the derivative does not get too small (leading to division by a small number) helps avoid large steps, which can prevent divergence.

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Math Problem Analysis

Mathematical Concepts

Newton's Method
Taylor Polynomial
Derivatives
Approximations

Formulas

Newton's Method: x_(n+1) = x_n - f(x_n) / f'(x_n)
Taylor Polynomial: T_n(x) = a_0 + a_1(x - a) + a_2(x - a)^2 + a_3(x - a)^3

Theorems

Newton's Method Theorem
Taylor Series Expansion Theorem

Suitable Grade Level

College Level