Approaching 0: Rationalizing the Limit x→4 √x-4

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In summary, to avoid an undefined or zero answer for the limit of √(x-4) as x approaches 4, the original expression must be manipulated or simplified. Rationalizing the expression only results in x-4/√x+4, which still yields an undefined answer. Substituting 4 into the original expression also results in an undefined answer. This can be avoided by using first principles and epsilon-delta, rather than conjugates.
  • #1
heythere1010
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Homework Statement


lim x→4 √x-4
I need to do something so that it is not undefined or 0.

Homework Equations

The Attempt at a Solution


I tried rationalizing, but that just gave me x-4/√x+4, which would still result in an undefined answer.
 
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  • #2
What exactly is the problem?
 
  • #3
PeroK said:
What exactly is the problem?
If I sub in 4 from the beginning, I will get sqrt 0. I can't have that as my answer.
 
  • #4
heythere1010 said:
If I sub in 4 from the beginning, I will get sqrt 0. I can't have that as my answer.
Why not?
 
  • #5
PeroK said:
Why not?
I thought you would need to do something like conjugates for it.
 
  • #6
Not unless you have to prove it from first principles using epsilon-delta.
 

FAQ: Approaching 0: Rationalizing the Limit x→4 √x-4

What does the limit x→4 √x-4 approach?

The limit x→4 √x-4 approaches 0, as the x-value gets closer and closer to 4.

Why is it important to rationalize the limit x→4 √x-4?

Rationalizing the limit helps to simplify the expression and make it easier to evaluate the limit. It also allows us to find the exact value of the limit, rather than just an approximation.

How do you rationalize the limit x→4 √x-4?

To rationalize the limit x→4 √x-4, we can multiply the expression by its conjugate, which is √x+4. This will eliminate the radical in the numerator and allow us to evaluate the limit.

Can we apply the limit x→4 √x-4 to any function?

No, the limit x→4 √x-4 only applies to functions that have a rational or irrational exponent. It cannot be used for functions with a logarithmic or trigonometric exponent.

Is there a shortcut for evaluating the limit x→4 √x-4?

Yes, if the limit x→4 √x-4 is in the form of a rational function, we can use L'Hôpital's rule to evaluate it. This rule states that if the limit of the numerator and denominator both approach 0 or infinity, we can take the derivative of both and evaluate the new limit.

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