Solving Limit: x.log(x) - Indetermination

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In summary, the problem is to find the limit of [x.log(x)] as x approaches positive infinity. The logarithm is of base 10. While the limit tends to infinity, the product of x and log(x) becomes an indeterminate form. However, this form is not actually indeterminate as the product of two quantities that are getting larger will also tend to infinity. It is important to note that x.log(x) can be rewritten as [log(x)]/[1/x]. This form does not allow for the application of l'Hopital's rule.
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Ryhion
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Homework Statement



The problem is

Limit [x.log(x)]
x->+oo

Homework Equations



Consider Log being a logarithm of base 10

This will tend to +oo, but x.log(x) will become (oo).(oo) which is an indetermination I need to know how to solve the indetermination in this case

The Attempt at a Solution



Thanks for all help
 
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  • #2
[itex]\infty * \infty[/itex] is NOT an indeterminate form. If you have two quantities that are getting larger and larger, their product will, too. The limit is infinity.
 
  • #3
Bear in mind that
[tex] x\log(x) = \frac{\log(x)}{\frac{1}{x}}.[/tex]
Given that form, you can apply l'Hopital's rule.
 
  • #4
No, you can't. That becomes "infinity over 0" which, again, is NOT an "indeterminant". L'Hopilal's rule does not apply and you don't need it.
 
  • #5
HallsofIvy said:
No, you can't. That becomes "infinity over 0" which, again, is NOT an "indeterminant". L'Hopilal's rule does not apply and you don't need it.

My apologies; read it too quickly and thought we were talking about a limit as x->0+.
 

FAQ: Solving Limit: x.log(x) - Indetermination

What is a limit?

A limit is a fundamental concept in calculus that describes the behavior of a function as its input approaches a certain value. It is the value that the function is approaching, rather than the actual value at that point.

What is an indeterminate form?

An indeterminate form is an expression that cannot be evaluated to a specific value, typically because it involves dividing by zero or taking the logarithm of zero. In these cases, further analysis is needed to determine the limit of the expression.

How do you solve a limit involving x.log(x)?

To solve this type of limit, you can use L'Hospital's rule, which states that the limit of a quotient of two functions is equal to the limit of their derivatives. In this case, you would take the derivative of both the numerator (x.log(x)) and denominator (1) to simplify the expression and then evaluate the limit again.

What is the result of solving the limit x.log(x)?

The result of solving this limit is 0. This can be determined by using L'Hospital's rule, as the derivative of x.log(x) is equal to 1 + log(x) and the derivative of 1 is 0. Therefore, the limit is equal to 0/1, which simplifies to 0.

Why is solving this limit important?

Solving limits is important in mathematics and science because it helps us understand the behavior of functions and make predictions about their values. In this case, solving the limit x.log(x) allows us to find the behavior of the logarithmic function as x approaches 0, which can have practical applications in areas such as finance, physics, and engineering.

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