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For the following indefinite integral, find the full power series centered at x=0 and then give the first 5 nonzero terms of the power series.

f(x)=∫x9cos(x3) dx


Sagot :

Space

Answer:

a.  [tex]\displaystyle f(x) = \sum^{\infty}_{n = 0} \frac{(-1)^n x^{6n + 10}}{(2n)!} + C_1[/tex]

b.  [tex]\displaystyle P_5(x) = \frac{x^{10}}{10} - \frac{x^{16}}{16 \cdot 2!} + \frac{x^{22}}{22 \cdot 4!} - \frac{x^{28}}{28 \cdot 6!} + \frac{x^{34}}{34 \cdot 8!} + C_1[/tex]

General Formulas and Concepts:

Calculus

Differentiation

  • Derivatives
  • Derivative Notation

Integration

  • Integrals
  • Indefinite Integrals
  • Integration Constant C

Integration Rule [Reverse Power Rule]:                                                               [tex]\displaystyle \int {x^n} \, dx = \frac{x^{n + 1}}{n + 1} + C[/tex]

Sequences

Series

MacLaurin Polynomials

  • MacLaurin Polynomial:                                                                                 [tex]\displaystyle P_n(x) = \frac{f(0)}{0!} + \frac{f'(0)}{1!}x + \frac{f''(0)}{2!}x^2 + \frac{f'''(0)}{3!}x^3 + \cdots + \frac{f^n(0)}{n!}x^n + \cdots[/tex]
  • MacLaurin Series:                                                                                         [tex]\displaystyle P(x) = \sum^{\infty}_{n = 0} \frac{f^n(0)}{n!}x^n[/tex]

Power Series

  • Power Series of Elementary Functions
  • MacLaurin Polynomials
  • Taylor Polynomials

Integration of Power Series:

  1.  [tex]\displaystyle f(x) = \sum^{\infty}_{n = 0} a_n(x - c)^n[/tex]
  2.  [tex]\displaystyle \int {f(x)} \, dx = \sum^{\infty}_{n = 0} \frac{a_n(x - c)^{n + 1}}{n + 1} + C_1[/tex]

Step-by-step explanation:

*Note:

You could derive the Taylor Series for cos(x) using Taylor polynomials differentiation but usually you have to memorize it.

We are given and are trying to find the power series:

[tex]\displaystyle f(x) = \int {x^9cos(x^3)} \, dx[/tex]

We know that the power series for cos(x) is:

[tex]\displaystyle cos(x) = \sum^{\infty}_{n = 0} \frac{(-1)^n x^{2n}}{(2n)!}[/tex]

To find the power series for cos(x³), substitute in x = x³:

[tex]\displaystyle cos(x^3) = \sum^{\infty}_{n = 0} \frac{(-1)^n (x^3)^{2n}}{(2n)!}[/tex]

Simplifying it, we have:

[tex]\displaystyle cos(x^3) = \sum^{\infty}_{n = 0} \frac{(-1)^n x^{6n}}{(2n)!}[/tex]

Rewrite the original function:

[tex]\displaystyle f(x) = \int {x^9 \sum^{\infty}_{n = 0} \frac{(-1)^n x^{6n}}{(2n)!}} \, dx[/tex]

Rewrite the integrand by including the x⁹ in the power series:

[tex]\displaystyle f(x) = \int {\sum^{\infty}_{n = 0} \frac{(-1)^n x^{6n + 9}}{(2n)!}} \, dx[/tex]

Integrating the power series, we have:

[tex]\displaystyle f(x) = {\sum^{\infty}_{n = 0} \frac{(-1)^n x^{6n + 10}}{(6n + 10)(2n)!}} + C_1[/tex]

To find the first 5 nonzero terms of the power series, we simply expand it as a MacLaurin polynomial:

[tex]\displaystyle P_5(x) = {\sum^4_{n = 0} \frac{(-1)^n x^{6n + 10}}{(6n + 10)(2n)!}} + C_1 = \frac{x^{10}}{10} - \frac{x^{16}}{16 \cdot 2!} + \frac{x^{22}}{22 \cdot 4!} - \frac{x^{28}}{28 \cdot 6!} + \frac{x^{34}}{34 \cdot 8!} + C_1[/tex]

Topic: AP Calculus BC (Calculus I + II)

Unit: Power Series

Book: College Calculus 10e