Find Value of k for Limit: x^3-6 / x^k+3

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Homework Statement



find the value of k such that the limit exists. lim xgoes to infinity (x^3-6)/(x^k+3).


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The Attempt at a Solution



I multiply both sides by 1/x^3 I get 1 in the numerator and x^k/x^3 in the denominator. I don't know what to next.
 
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x^k/x^3 is x^(k-3). Consider the cases of k>3, k<3 and k=3.
 
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