Chapter 9: Problem 1
Find the Taylor polynomials of orders \(0,1,2,\) and 3 generated by \(f\) at \(a\) $$f(x)=e^{2 x}, \quad a=0$$
Short Answer
Expert verified
\(P_0(x) = 1\); \(P_1(x) = 1 + 2x\); \(P_2(x) = 1 + 2x + 2x^2\); \(P_3(x) = 1 + 2x + 2x^2 + \frac{4}{3}x^3\).
Step by step solution
01
Understanding Taylor Polynomials
The Taylor polynomial of order n for a function \(f(x)\) centered at \(a\) is given by \(P_n(x) = f(a) + f'(a)(x-a) + \frac{f''(a)}{2!}(x-a)^2 + \frac{f'''(a)}{3!}(x-a)^3 + \ldots + \frac{f^{(n)}(a)}{n!}(x-a)^n\). To solve this, we need to find the successive derivatives of \(f(x)=e^{2x}\) and evaluate them at \(x=0\).
02
Compute and evaluate f(a)
Calculate \(f(x)\) at \(x=0\). We know that \(f(x) = e^{2x},\) so \(f(0) = e^{0} = 1\).
03
Find f'(x) and evaluate f'(a)
Differentiate \(f(x) = e^{2x}\) with respect to \(x\). We know \(f'(x) = \frac{d}{dx}(e^{2x}) = 2e^{2x}\). Thus, \(f'(0) = 2e^0 = 2\).
04
Find f''(x) and evaluate f''(a)
Differentiate \(f'(x) = 2e^{2x}\) with respect to \(x\). We have \(f''(x) = \frac{d}{dx}(2e^{2x}) = 4e^{2x}\). Thus, \(f''(0) = 4e^0 = 4\).
05
Find f'''(x) and evaluate f'''(a)
Differentiate \(f''(x) = 4e^{2x}\) with respect to \(x\). This gives us \(f'''(x) = \frac{d}{dx}(4e^{2x}) = 8e^{2x}\). Thus, \(f'''(0) = 8e^0 = 8\).
06
Construct P_0(x)
The zeroth order Taylor polynomial is simply \(P_0(x) = f(0) = 1\).
07
Construct P_1(x)
The first-order Taylor polynomial uses the first derivative: \(P_1(x) = f(0) + f'(0)x = 1 + 2x\).
08
Construct P_2(x)
The second order Taylor polynomial uses up to the second derivative: \(P_2(x) = f(0) + f'(0)x + \frac{f''(0)}{2!}x^2 = 1 + 2x + \frac{4}{2}x^2 = 1 + 2x + 2x^2\).
09
Construct P_3(x)
The third order Taylor polynomial is: \(P_3(x) = f(0) + f'(0)x + \frac{f''(0)}{2!}x^2 + \frac{f'''(0)}{3!}x^3 = 1 + 2x + 2x^2 + \frac{8}{6}x^3 = 1 + 2x + 2x^2 + \frac{4}{3}x^3\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivatives
Derivatives are fundamental tools in calculus, representing the rate at which a function changes. To understand Taylor polynomials, it's essential to grasp derivatives because they help describe how a function behaves at a certain point. In this exercise, we work with the function \(f(x) = e^{2x}\). To construct Taylor polynomials, we calculate derivatives up to the desired order and evaluate them at the specific point \(a = 0\). Here's a quick overview of the process:
- First, find the function's value at \(x = 0\): \(f(0) = 1\).
- Next, differentiate the function to find \(f'(x) = 2e^{2x}\), and evaluate \(f'(0) = 2\).
- Then, calculate the second derivative: \(f''(x) = 4e^{2x}\), and evaluate \(f''(0) = 4\).
- Finally, determine the third derivative: \(f'''(x) = 8e^{2x}\), with \(f'''(0) = 8\).
Exponential Functions
Exponential functions are crucial in many areas of mathematics and science due to their unique properties. The function \(f(x) = e^{2x}\) is an example where the base \(e\) is Euler's number, approximately 2.71828. This function grows exponentially, meaning it increases at a constantly proportional rate.Some key characteristics of exponential functions like \(e^{2x}\) include:
- The derivative of \(e^{2x}\) provides the same function up to a constant multiple. This makes exponential functions straightforward to differentiate repeatedly.
- The exponential function is continuous and smooth, with no breaks or corners.
- Exponential functions have a constant ratio of change rather than a constant amount of change.
Maclaurin Series
The Maclaurin series is a special case of a Taylor series, where the center point \(a = 0\). It makes the expansion around \(x = 0\) particularly efficient for functions like \(e^{2x}\). The general form of a Maclaurin series for a function \(f(x)\) is:\[P_n(x) = f(0) + f'(0)x + \frac{f''(0)}{2!}x^2 + \frac{f'''(0)}{3!}x^3 + \ldots + \frac{f^{(n)}(0)}{n!}x^n\]In our exercise, the task was to find the Maclaurin series' Taylor polynomials up to the third order. Let's summarize:
- The zeroth-order approximation or \(P_0(x)\) is simply the constant term \(f(0) = 1\).
- The first-order polynomial or \(P_1(x)\) includes the linear term: \(1 + 2x\).
- The second-order polynomial, \(P_2(x)\), adds a quadratic term: \(1 + 2x + 2x^2\).
- The third-order polynomial or \(P_3(x)\) introduces the cubic term: \(1 + 2x + 2x^2 + \frac{4}{3}x^3\).