Calculus 2 Series Question: Prove the inequality

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SUMMARY

The discussion focuses on proving the inequality \(\frac{1}{2} - \frac{x^2}{24} < \frac{1 - \cos x}{x^2} < \frac{1}{2}\) using the Maclaurin series for \(\cos x\) and the Alternating Series Estimation Theorem. The Maclaurin series for \(\cos x\) is given by \(\sum_{n=0}^\infty \frac{x^{2n}(-1)^{n}}{(2n)!}\). The error in the approximation is defined as \(|error| < \frac{x^{2n+2}}{(2n + 2)!}\), which is crucial for establishing the bounds of the inequality.

PREREQUISITES
  • Understanding of Maclaurin series and their applications
  • Familiarity with the Alternating Series Estimation Theorem
  • Basic knowledge of calculus, specifically limits and inequalities
  • Ability to manipulate series and factorial expressions
NEXT STEPS
  • Study the derivation and applications of the Maclaurin series for trigonometric functions
  • Explore the Alternating Series Estimation Theorem in detail
  • Practice proving inequalities involving series expansions
  • Learn about convergence tests for series in calculus
USEFUL FOR

Students in calculus courses, particularly those studying series and approximations, as well as educators seeking to enhance their understanding of series convergence and error estimation techniques.

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This was already posted by someone else but an answer wasn't received so I thought I'd repost. Any help is appreciated.

Homework Statement



Use the Maclaurin series for cosx and the Alternating Series Estimation Theorem to show that

[tex]\frac{1}{2} - \frac{x^2}{24} < \frac{1-cosx}{x^2} < \frac{1}{2}[/tex]


Homework Equations



[tex] <br /> cosx = 1 - \frac{x^2}{2} + \frac{x^4}{4} - \cdot \cdot \cdot = \sum_{n=0}^\infty \frac{x^{2n}(-1)^{n}}{(2n)!} <br /> [/tex]


The Attempt at a Solution



Using the Alternating Series Estimation Theorem I know the error is less than the next term:

[tex] |error| < \frac{x^{2n+2}}{(2n + 2)!}[/tex]

I have no idea how to answer this.
 
Last edited:
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Can you prove that

[tex]1-\frac{x^2}{2}<\cos(x)<1-\frac{x^2}{2}+\frac{x^4}{24}[/tex]
 

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