Rationalizing the Numerator to Evaluate a Limit for a Tough Function

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SUMMARY

The discussion focuses on evaluating the limit of the function (x^(1/3) - a^(1/3))/(x - a) as x approaches a. Participants suggest using the identity for the difference of cubes, (A^3 - B^3) = (A - B)(A^2 + AB + B^2), where A = x^(1/3) and B = a^(1/3), to factor out (x - a) from the numerator. An alternative method involves rationalizing the numerator by multiplying both the numerator and denominator by (x^(2/3) + a^(1/3)x^(1/3) + a^(2/3)). This approach effectively simplifies the limit evaluation.

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Evaluate lim as x approaches a for (x^1/3 - a^1/3)/(x-a). I want to factor out x-a from the numerator so that the denominator is not equal to zero. How can I do this?
 
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(A^3-B^3)=(A-B)(A^2+AB+B^2). Use that formula where A=x^(1/3) and B=a^(1/3). I.e. factor (x-a).
 
Another way to do that (Dick's hint is perfectly good) is not to factor but to multiply to rationalize the numerator. Using the same formula Dick gave, x- a= (x1/3- a1/3)(x2/3+ a1/3x1/3+ a2/3). Multiply both numerator and denominator by that.
 

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