Limit of x^2/(1-cosx) as x→0 - Solution without LH Rule

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SUMMARY

The limit of x^2/(1-cos(x)) as x approaches 0 is determined to be 2 without using L'Hôpital's rule. The solution utilizes the trigonometric identity cos(x) = 1 - 2sin^2(x/2) and the limit property lim_{x→0} (x/sin(x)) = 1. Additionally, multiplying both the numerator and denominator by (1 + cos(x)) simplifies the expression, leading to the conclusion.

PREREQUISITES
  • Understanding of trigonometric identities, specifically cos(x) and sin(x).
  • Familiarity with limits and continuity in calculus.
  • Knowledge of power series expansions, particularly for trigonometric functions.
  • Basic algebraic manipulation skills for simplifying expressions.
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  • Study the derivation and applications of the limit lim_{x→0} (x/sin(x)).
  • Explore trigonometric identities and their proofs, focusing on cos(x) and sin(x).
  • Learn about power series expansions for various functions, including sin(x) and cos(x).
  • Investigate alternative methods for evaluating limits without L'Hôpital's rule.
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Students studying calculus, particularly those focusing on limits and trigonometric functions, as well as educators seeking alternative teaching methods for limit evaluation.

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Homework Statement



Find the limit as x approaches 0 of x^2/(1-cosx).

Homework Equations



None.

The Attempt at a Solution



I know from L'Hopital's rule that the limit is 2, but I'm not supposed to use L'Hopital's rule to calculate it. What else can I do here?
 
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How about the identity cos(x) = 1 - 2sin^2(x/2)?
 
You could also consider the power series expansion of cos(x) around zero.
 
Multiply both numerator and denominator by 1+ cos(x). Then use the fact that
lim_{x\rightarrow 0}\frac{x}{sin(x)}= 1.
 

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