I can't make an arrow for "approaches" easy using 
the software here, so please interpret  
as though it were  → .


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We need to get that exponent 3 outside the limit.
First get it outside the parentheses:

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Then get it outside the limit:

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Now with that 3 exponent outside the limit, we can use 
l'Hopital's rule on the inside without it:

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Multiply numerator and denominator both by 

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Edwin