Chapter 4: Problem 4
Use Newton's method to estimate the two zeros of the function \(f(x)=2 x-x^{2}+1 .\) Start with \(x_{0}=0\) for the left-hand zero and with \(x_{0}=2\) for the zero on the right. Then, in each case, find \(x_{2}\).
Short Answer
Expert verified
The second iterations are \( x_2 = -0.583 \) for the left-hand zero, and \( x_2 = 2.417 \) for the right-hand zero.
Step by step solution
01
Find the Derivative of the Function
To apply Newton's method, we need to find the first derivative of the function. Given the function \[ f(x) = 2x - x^2 + 1, \]we differentiate it to get:\[ f'(x) = 2 - 2x. \]
02
Apply Newton's Method Formula
Newton's method is given by the iterative formula:\[ x_{n+1} = x_n - \frac{f(x_n)}{f'(x_n)}. \] We'll use this formula to find approximations for the zeros of the function on each interval.
03
Find the First Iteration for the Left-Hand Zero
Start with the initial guess \( x_0 = 0 \). Calculate \( x_1 \) using the formula:\[ x_1 = x_0 - \frac{f(x_0)}{f'(x_0)} = 0 - \frac{f(0)}{f'(0)}.\]Substitute \( f(0) = 2(0) - 0^2 + 1 = 1 \) and \( f'(0) = 2 - 2(0) = 2 \), giving:\[ x_1 = 0 - \frac{1}{2} = -0.5. \]
04
Find the Second Iteration for the Left-Hand Zero
Now with \( x_1 = -0.5 \), find \( x_2 \):\[ x_2 = x_1 - \frac{f(x_1)}{f'(x_1)} = -0.5 - \frac{f(-0.5)}{f'(-0.5)}.\]Calculate \( f(-0.5) = 2(-0.5) - (-0.5)^2 + 1 = 0.25 \) and \( f'(-0.5) = 2 + 1 = 3 \):\[ x_2 = -0.5 - \frac{0.25}{3} \approx -0.583. \]
05
Find the First Iteration for the Right-Hand Zero
Start with the initial guess \( x_0 = 2 \). Calculate \( x_1 \):\[ x_1 = x_0 - \frac{f(x_0)}{f'(x_0)} = 2 - \frac{f(2)}{f'(2)}.\]Substitute \( f(2) = 2(2) - 2^2 + 1 = 1 \) and \( f'(2) = 2 - 4 = -2 \), giving:\[ x_1 = 2 - \frac{1}{-2} = 2.5.\]
06
Find the Second Iteration for the Right-Hand Zero
Now with \( x_1 = 2.5 \), find \( x_2 \):\[ x_2 = x_1 - \frac{f(x_1)}{f'(x_1)} = 2.5 - \frac{f(2.5)}{f'(2.5)}.\]Calculate \( f(2.5) = 2(2.5) - (2.5)^2 + 1 = -0.25 \) and \( f'(2.5) = 2 - 5 = -3 \):\[ x_2 = 2.5 - \frac{-0.25}{-3} = 2.5 + 0.083 \approx 2.417.\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivative of Function
Understanding derivatives is essential for many calculus applications, including Newton's Method. A derivative represents the rate at which a function is changing at any given point. It's essentially the slope of the tangent line to the curve at a particular location. When handling the function \( f(x) = 2x - x^2 + 1 \), the process of differentiation gives us \( f'(x) = 2 - 2x \). This derivative is key to Newton's Method because it allows us to determine how sharply the function is climbing or descending at a point. By calculating \( f'(x) \), we can effectively make predictions about how to adjust our estimates in Newton's iterative process.
Iterative Formula
Newton's Method relies on a specific iterative formula. This formula is beautifully simple yet powerful for numerical approximations. Defined as:
- \( x_{n+1} = x_n - \frac{f(x_n)}{f'(x_n)} \)
- \( x_n \) is our current estimate of the root.
- \( f(x_n) \) is the value of the function at \( x_n \).
- \( f'(x_n) \) provides the slope at that point.
- The fraction \( \frac{f(x_n)}{f'(x_n)} \) tells us how much to correct our current estimate.
Approximating Zeros
Approximating zeros means finding values of \( x \) where the function \( f(x) \) equals zero. These are the points where the graph of the function touches or crosses the x-axis. For the function \( f(x) = 2x - x^2 + 1 \), we employed Newton's Method starting with initial guesses at 0 and 2. Through consecutive iterations, our approximations for the zeros became more precise:
- Beginning with \( x_0 = 0 \), the next estimation \( x_1 \) was \(-0.5\), and further refined to \( x_2 = -0.583\).
- For \( x_0 = 2 \), the first adjustment provided \( x_1 = 2.5 \), followed by \( x_2 = 2.417\).
Calculus Problem Solving
Calculus offers various methodologies for solving complex problems, one of which is using Newton's Method to find function zeros. The process involves several calculus concepts:
- First, compute the derivative to understand the function's behavior.
- Next, apply Newton's iterative formula to find a zero.
- Each iteration refines the approximation, gradually converging to a solution.