Limit of x*cot(x)-1/x^2 as x->0

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SUMMARY

The limit of the expression x*cot(x) - 1/x^2 as x approaches 0 evaluates to 0. The discussion highlights that applying L'Hôpital's rule may not yield straightforward results due to the indeterminate form. Instead, substituting cot(x) with cos(x)/sin(x) and expanding the functions using power series for sin(x) and cos(x) provides a clearer path to the solution. The key takeaway is that deeper function expansion is necessary to resolve the limit correctly.

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tsuwal
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Homework Statement


limit x*cot(x)-1/x^2
x->0



Homework Equations


lim x*cot(x)=1
x->0




The Attempt at a Solution


it's an indetermination but L'hopital rule doesn't help very much..
 
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tsuwal said:

Homework Statement


limit x*cot(x)-1/x^2
x->0



Homework Equations


lim x*cot(x)=1
x->0




The Attempt at a Solution


it's an indetermination but L'hopital rule doesn't help very much..

Sometimes l'Hopital works better if you try rearranging things. Substitute cot(x)=cos(x)/sin(x). Multiply numerator and denominator by sin(x) and try again.
 
tsuwal said:
limit x*cot(x)-1/x^2
x->0
I assume you mean limit (x*cot(x)-1)/x2 as x->0.
The indeterminacy simply means you've not gone far enough in the expansion of the functions as power series. What expansions do you know for tan x, or failing that, for sin x and cos x?
 
thanks Dick, i wish i could see the those simplifications right away!
 

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