Math Problem Statement

From analyzing the graph of the function e^x - 2x - 4, we see that the equation e^x - 2x - 4 = 0 has exactly two solutions, one positive and the other negative. We wish to estimate the negative solution using Newton’s Method, starting with x_0 = 0. What are the successive approximations x_1, x_2, and x_3?

Solution

To solve this problem using Newton's Method, we need to iteratively calculate xnx_n using the formula:

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

Step 1: Define f(x)f(x) and f(x)f'(x)

The function given is:

f(x)=ex2x4f(x) = e^x - 2x - 4

The derivative is:

f(x)=ex2f'(x) = e^x - 2

Step 2: Start with x0=0x_0 = 0

We are given the initial guess x0=0x_0 = 0. Now we compute the next approximations.

Iteration 1: Compute x1x_1

x1=x0f(x0)f(x0)x_1 = x_0 - \frac{f(x_0)}{f'(x_0)}

Substitute x0=0x_0 = 0 into f(x)f(x) and f(x)f'(x):

f(0)=e02(0)4=14=3f(0) = e^0 - 2(0) - 4 = 1 - 4 = -3 f(0)=e02=12=1f'(0) = e^0 - 2 = 1 - 2 = -1

x1=031=03=3x_1 = 0 - \frac{-3}{-1} = 0 - 3 = -3

Iteration 2: Compute x2x_2

x2=x1f(x1)f(x1)x_2 = x_1 - \frac{f(x_1)}{f'(x_1)}

Substitute x1=3x_1 = -3 into f(x)f(x) and f(x)f'(x):

f(3)=e32(3)4=e3+64=e3+2f(-3) = e^{-3} - 2(-3) - 4 = e^{-3} + 6 - 4 = e^{-3} + 2 f(3)=e32f'(-3) = e^{-3} - 2

Using a calculator:

e30.0498e^{-3} \approx 0.0498

f(3)0.0498+2=2.0498f(-3) \approx 0.0498 + 2 = 2.0498 f(3)0.04982=1.9502f'(-3) \approx 0.0498 - 2 = -1.9502

x2=32.04981.95023+1.0513=1.9487x_2 = -3 - \frac{2.0498}{-1.9502} \approx -3 + 1.0513 = -1.9487

Iteration 3: Compute x3x_3

x3=x2f(x2)f(x2)x_3 = x_2 - \frac{f(x_2)}{f'(x_2)}

Substitute x2=1.9487x_2 = -1.9487 into f(x)f(x) and f(x)f'(x):

f(1.9487)=e1.94872(1.9487)4f(-1.9487) = e^{-1.9487} - 2(-1.9487) - 4 f(1.9487)=e1.94872f'(-1.9487) = e^{-1.9487} - 2

Using a calculator:

e1.94870.1420e^{-1.9487} \approx 0.1420

f(1.9487)0.1420+2(1.9487)4=0.14203.897441.7554f(-1.9487) \approx 0.1420 + 2(-1.9487) - 4 = 0.1420 - 3.8974 - 4 \approx -1.7554 f(1.9487)0.142021.858f'(-1.9487) \approx 0.1420 - 2 \approx -1.858

x3=1.94871.75541.8581.9487+0.9447=1.0040x_3 = -1.9487 - \frac{-1.7554}{-1.858} \approx -1.9487 + 0.9447 = -1.0040

Final Answers:

x1=3.00000,x2=1.94870,x3=1.00400x_1 = -3.00000, \quad x_2 = -1.94870, \quad x_3 = -1.00400

Would you like detailed explanations for these steps or assistance with other related concepts?


5 Questions to Explore Further:

  1. What are the theoretical foundations of Newton's Method?
  2. How does the choice of the initial guess (x0x_0) affect convergence?
  3. Can Newton's Method fail to converge? If so, under what conditions?
  4. How does this method compare with other root-finding algorithms (e.g., bisection)?
  5. Can we use Newton's Method for systems of equations? How?

Tip: Always ensure the derivative f(x)0f'(x) \neq 0 at any point during Newton's Method to avoid division by zero.

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Math Problem Analysis

Mathematical Concepts

Calculus
Root-finding
Newton's Method
Exponential Functions

Formulas

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

Theorems

Newton's Method for Approximating Roots

Suitable Grade Level

Grades 11-12, College Level