Chapter 10: Problem 49
Give an example of: A function with a Taylor series whose third-degree term is zero.
Short Answer
Expert verified
The function \( f(x) = x^4 \) has a Taylor series with a zero third-degree term at \( x=0 \).
Step by step solution
01
Introduction to Taylor Series
A Taylor series is an infinite sum of terms calculated from the values of a function's derivatives at a single point. It is expressed as: \[ f(x) = f(a) + f'(a)(x-a) + \frac{f''(a)}{2!}(x-a)^2 + \frac{f'''(a)}{3!}(x-a)^3 + \cdots \] where the coefficients involve the derivatives of the function \( f \) evaluated at the point \( a \).
02
Identifying the Third-Degree Term
The third-degree term in the Taylor series expansion is \( \frac{f'''(a)}{3!}(x-a)^3 \). To make this term zero, we need \( f'''(a) = 0 \). This means the third derivative of the function at the point \( a \) must be zero.
03
Choosing a Function
Let's consider the function \( f(x) = x^4 \). We know that the derivatives of \( f(x) \) are \( f'(x) = 4x^3 \), \( f''(x) = 12x^2 \), and \( f'''(x) = 24x \).
04
Evaluating the Third Derivative
Evaluate \( f'''(x) \) at \( a = 0 \) to check if it's zero: \[ f'''(0) = 24 \times 0 = 0 \] Hence, the third-degree term in the Taylor series expanding around \( a = 0 \) is zero.
05
Confirming the Taylor Series
The Taylor series expansion of \( f(x) = x^4 \) around \( x = 0 \) is: \( f(0) + f'(0)x + \frac{f''(0)}{2!}x^2 + \frac{f'''(0)}{3!}x^3 + \cdots = 0 + 0 + 0 + 0 + \cdots + \frac{f^{(4)}(0)}{4!}x^4 + \cdots \), confirming the third-degree term is zero.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Calculus
Calculus is a branch of mathematics that studies how things change. It provides tools to analyze continuous change and is foundational for understanding advanced mathematical concepts.
There are two major parts of calculus:
There are two major parts of calculus:
- Differential Calculus - This focuses on the concept of the derivative, which represents rates of change and slopes of curves.
- Integral Calculus - This deals with the concept of integration, which is about the accumulation of quantities and areas under curves.
Degree of a Polynomial
The degree of a polynomial is the highest power of the variable in the expression that has a non-zero coefficient. It tells us a lot about the behavior of the polynomial function, especially as the input variable grows larger or smaller.
- A polynomial such as \( a_nx^n + a_{n-1}x^{n-1} + \cdots + a_1x + a_0 \) has degree \( n \), where \( a_n eq 0 \).
- The degree determines the maximum number of roots the polynomial can have.
- It also establishes the end behavior of the function.
Derivative
A derivative represents the rate at which a function changes at any point. It is a central concept in differential calculus, providing insights into the slope of a function and how changes in input affect the output.
- The first derivative \( f'(x) \) gives the slope of the tangent line to the graph at any point \( x \).
- The second derivative \( f''(x) \) indicates concavity or convexity of the function and can be used to find points of inflection.
- The third derivative \( f'''(x) \), as shown in the solution, affects the third-degree term of the Taylor expansion.
Function Expansion
Expanding a function into a series allows us to approximate it using simpler polynomial expressions. This is crucial when dealing with complex functions that are hard to analyze directly.
- The Taylor series is one method of function expansion. It uses derivatives at a point to express the function as an infinite sum of terms.
- The third-degree polynomial component in a Taylor series provides information about the function's behavior close to a point, up to cubic changes.
- By choosing points where certain derivatives are zero, we can simplify expansions, as shown in the example where the third-degree term is zero.