Chapter 10: Problem 25
Find the Taylor series generated by \(f\) at \(x=a\). $$f(x)=x^{4}+x^{2}+1, \quad a=-2$$
Short Answer
Expert verified
The Taylor series is \(T(x) = 21 - 36(x + 2) + 25(x + 2)^2 - 8(x + 2)^3 + (x + 2)^4\).
Step by step solution
01
Identify the Formula for a Taylor Series
The Taylor series of a function \(f(x)\) about a point \(x = a\) is given by \( T(x) = f(a) + f'(a)(x-a) + \frac{f''(a)}{2!}(x-a)^2 + \frac{f'''(a)}{3!}(x-a)^3 + \ldots \). This means we will need the derivatives of \(f(x)\) evaluated at \(x = a\).
02
Calculate the Function Value at \(x = -2\)
Substitute \(x = -2\) into \(f(x) = x^4 + x^2 + 1\) to find \(f(-2)\). Calculate: \((-2)^4 + (-2)^2 + 1 = 16 + 4 + 1 = 21\). So, \(f(-2) = 21\).
03
Find the First Derivative and Evaluate at \(x = -2\)
Differentiate to find \(f'(x) = 4x^3 + 2x\). Substitute \(x = -2\) to find \(f'(-2) = 4(-2)^3 + 2(-2) = -32 - 4 = -36\).
04
Find the Second Derivative and Evaluate at \(x = -2\)
Differentiate again to find \(f''(x) = 12x^2 + 2\). Substitute \(x = -2\) to get \(f''(-2) = 12(-2)^2 + 2 = 48 + 2 = 50\).
05
Find the Third Derivative and Evaluate at \(x = -2\)
Differentiate once more to obtain \(f'''(x) = 24x\). Calculate \(f'''(-2) = 24(-2) = -48\).
06
Find the Fourth Derivative and Evaluate at \(x = -2\)
Differentiating once again results in \(f^{(4)}(x) = 24\). Therefore, \(f^{(4)}(-2) = 24\).
07
Write the Taylor Series Expansion
Using the results from the previous steps, substitute into the Taylor series formula: \[T(x) = 21 - 36(x + 2) + \frac{50}{2!}(x + 2)^2 - \frac{48}{3!}(x + 2)^3 + \frac{24}{4!}(x + 2)^4.\] Simplifying gives: \[T(x) = 21 - 36(x + 2) + 25(x + 2)^2 - 8(x + 2)^3 + 1(x + 2)^4.\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polynomial Functions
Polynomial functions form a crucial part of mathematics, especially in calculus and algebra. A polynomial function is an expression made up of variables, coefficients, and the operations of addition, subtraction, multiplication, and non-negative integer exponents.
- They are expressed in the form: \( f(x) = a_nx^n + a_{n-1}x^{n-1} + \ldots + a_1x + a_0 \), where each \( a \) is a coefficient and \( n \) is the degree of the polynomial.
- The degree of the polynomial is determined by the highest exponent present, which influences the curve's shape and end behavior.
- For example, the function \( f(x) = x^4 + x^2 + 1 \) is a polynomial of degree 4, known as a quartic polynomial.
Derivatives
Derivatives are a fundamental concept in calculus that measure how a function changes as its input changes. If you're familiar with slopes of lines, derivatives take this idea further by dealing with curves.
- They provide the rate of change or the slope of the tangent line to the curve at a specific point.
- To find derivatives, you apply the differentiation rules, like the power rule, product rule, or chain rule, depending on the function's complexity.
- For a polynomial like \( f(x) = x^4 + x^2 + 1 \), differentiating would give \( f'(x) = 4x^3 + 2x \).
Mathematical Modeling
Mathematical modeling involves simplifying and representing real-world scenarios through mathematical expressions and formulas. It's about crafting a mathematical representation that can describe and predict outcomes in real-life situations.
- Taylor series act as an effective mathematical model because they approximate complex functions using polynomials, which are much simpler to work with.
- They can model natural phenomena where functions are too complicated to handle in their original forms.
- By expanding a function into its Taylor series around a point \( a \), the series allows the function to be expressed as an infinite sum of terms.