Math Problem Statement

please solve this

please solve this

Solution

Let's solve the problem step by step.


Part (a): Identify f(x)f(x) and x0x_0

The function f(x)f(x) for linear approximation needs to satisfy the relationship:

31243f(x0)+f(x0)(xx0)\sqrt[3]{3124} \approx f(x_0) + f'(x_0)(x - x_0)

The choice of f(x)f(x) is f(x)=x3=x1/3f(x) = \sqrt[3]{x} = x^{1/3}.
The given x0x_0 is 3125 because it's close to 3124 and its cube root is easy to compute (31253=15\sqrt[3]{3125} = 15).

f(x)=x1/3,x0=3125f(x) = x^{1/3}, \quad x_0 = 3125


Part (b): Linear approximation of 31243\sqrt[3]{3124}

Using the formula for linear approximation:

f(x)f(x0)+f(x0)(xx0)f(x) \approx f(x_0) + f'(x_0)(x - x_0)

  1. Compute f(x0)=31253=15f(x_0) = \sqrt[3]{3125} = 15.
  2. Derivative: f(x)=13x2/3f'(x) = \frac{1}{3}x^{-2/3}, so f(x0)=13(3125)2/3=13152=1675f'(x_0) = \frac{1}{3}(3125)^{-2/3} = \frac{1}{3 \cdot 15^2} = \frac{1}{675}.
  3. Substitute x=3124x = 3124:

f(3124)15+1675(31243125)=151675=150.00148=14.99852f(3124) \approx 15 + \frac{1}{675}(3124 - 3125) = 15 - \frac{1}{675} = 15 - 0.00148 = 14.99852

Thus: 3124314.9985\sqrt[3]{3124} \approx 14.9985


Part (c): Choose g(x)g(x) for Newton's Method

Newton's Method approximates roots of functions. To approximate 31243\sqrt[3]{3124}, we define g(x)g(x) such that g(31243)=0g(\sqrt[3]{3124}) = 0.
The obvious choice is:

g(x)=x33124g(x) = x^3 - 3124


Part (d): Choose x0x_0 (initial guess for Newton's Method)

To find an integer x0x_0 close to 31243\sqrt[3]{3124}, consider 31253=15\sqrt[3]{3125} = 15. Thus:

x0=15x_0 = 15


Part (e): Perform two iterations of Newton's Method

Newton's Method formula is:

xn+1=xng(xn)g(xn)x_{n+1} = x_n - \frac{g(x_n)}{g'(x_n)}

For g(x)=x33124g(x) = x^3 - 3124, we have g(x)=3x2g'(x) = 3x^2. Starting with x0=15x_0 = 15:

First Iteration:

x1=x0g(x0)g(x0)=1515331243152x_1 = x_0 - \frac{g(x_0)}{g'(x_0)} = 15 - \frac{15^3 - 3124}{3 \cdot 15^2}

  1. Compute g(15)=1533124=33753124=251g(15) = 15^3 - 3124 = 3375 - 3124 = 251.
  2. Compute g(15)=3152=3225=675g'(15) = 3 \cdot 15^2 = 3 \cdot 225 = 675.
  3. Substitute:

x1=15251675=150.3719=14.6281x_1 = 15 - \frac{251}{675} = 15 - 0.3719 = 14.6281

Second Iteration:

x2=x1g(x1)g(x1)x_2 = x_1 - \frac{g(x_1)}{g'(x_1)}

  1. Compute g(14.6281)=(14.6281)33124g(14.6281) = (14.6281)^3 - 3124: 14.628133125.854sog(14.6281)=3125.8543124=1.85414.6281^3 \approx 3125.854 \quad \text{so} \quad g(14.6281) = 3125.854 - 3124 = 1.854
  2. Compute g(14.6281)=3(14.6281)2g'(14.6281) = 3 \cdot (14.6281)^2: 14.62812214.082,sog(14.6281)=3214.082=642.24614.6281^2 \approx 214.082, \quad \text{so} \quad g'(14.6281) = 3 \cdot 214.082 = 642.246
  3. Substitute:

x2=14.62811.854642.246=14.62810.00289=14.6252x_2 = 14.6281 - \frac{1.854}{642.246} = 14.6281 - 0.00289 = 14.6252

Thus, after two iterations: x114.6281,x214.6252x_1 \approx 14.6281, \quad x_2 \approx 14.6252


Final Answers:

(a) f(x)=x1/3,x0=3125f(x) = x^{1/3}, \, x_0 = 3125
(b) 3124314.9985\sqrt[3]{3124} \approx 14.9985
(c) g(x)=x33124g(x) = x^3 - 3124
(d) x0=15x_0 = 15
(e) x114.6281,x214.6252x_1 \approx 14.6281, \, x_2 \approx 14.6252


Would you like detailed steps for any part or further clarifications?

Related Questions:

  1. How does linear approximation differ from Newton's Method?
  2. Why is f(x)=x1/3f(x) = x^{1/3} chosen in this problem?
  3. How is the derivative f(x)f'(x) calculated for x1/3x^{1/3}?
  4. What happens if x0x_0 is not close to the true root in Newton's Method?
  5. How can the accuracy of Newton's Method be increased?

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

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Math Problem Analysis

Mathematical Concepts

Linear Approximation
Newton's Method
Cube Root
Derivatives

Formulas

Linear Approximation Formula: f(x) ≈ f(x₀) + f'(x₀)(x - x₀)
Newton's Method Formula: xₙ₊₁ = xₙ - g(xₙ) / g'(xₙ)
Derivative of x^(1/3): f'(x) = (1/3) * x^(-2/3)

Theorems

Linear Approximation Theorem
Newton's Method Convergence Theorem

Suitable Grade Level

Grades 11-12