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

In summary, the limit of x^2/(1-cosx) as x approaches 0 is 0. Finding this limit helps to understand the behavior of the function near the point x=0 and has implications in various mathematical applications. The process for solving this limit without using LH Rule involves simplifying the expression, using trigonometric identities, and making a substitution. It is important to know how to solve this limit without LH Rule as it can be useful in certain cases and helps to develop a deeper understanding of limits. Other methods for solving this limit include using the Maclaurin series expansion or L'Hopital's Rule, but the most commonly used method is factoring out the x and using trigonometric identities.
  • #1
Frillth
80
0

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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  • #2
How about the identity cos(x) = 1 - 2sin^2(x/2)?
 
  • #3
You could also consider the power series expansion of cos(x) around zero.
 
  • #4
Multiply both numerator and denominator by 1+ cos(x). Then use the fact that
[tex]lim_{x\rightarrow 0}\frac{x}{sin(x)}= 1[/tex].
 

What is the limit of x^2/(1-cosx) as x approaches 0?

The limit of x^2/(1-cosx) as x approaches 0 is 0.

What is the significance of finding the limit of x^2/(1-cosx) as x approaches 0?

Finding the limit of x^2/(1-cosx) as x approaches 0 helps to understand the behavior of the function near the point x=0, which can have implications in various mathematical applications.

What is the process for solving the limit of x^2/(1-cosx) as x approaches 0 without using LH Rule?

The process for solving the limit of x^2/(1-cosx) as x approaches 0 without using LH Rule involves simplifying the expression by factoring out the x and using trigonometric identities to eliminate the denominator. This results in the limit becoming x times the limit of x/(1-cosx) as x approaches 0. Then, using the substitution u=sinx, the limit can be rewritten as the limit of u/(1-u^2) as u approaches 0, which can be solved using basic algebra.

Why is it important to know how to solve the limit of x^2/(1-cosx) as x approaches 0 without using LH Rule?

Knowing how to solve the limit of x^2/(1-cosx) as x approaches 0 without using LH Rule can be useful in cases where LH Rule cannot be applied or when a more efficient and straightforward solution is desired. It also helps to develop a deeper understanding of the concept of limits and strengthens problem-solving skills in calculus.

Are there any other methods for solving the limit of x^2/(1-cosx) as x approaches 0?

Yes, there are other methods for solving the limit of x^2/(1-cosx) as x approaches 0, such as using the Maclaurin series expansion of cosx to rewrite the expression as a polynomial, or using L'Hopital's Rule in combination with trigonometric identities. However, the method of factoring out the x and using trigonometric identities is the most commonly used and straightforward method for solving this particular limit.

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