



 
Imad, What you need to recognize here is a difference of cubes
Thus if p is the cube root of 1 + x and r is the cube root of 1  x then the numerator of your fraction is the first factor in the difference of cubes expression above. Multiple the numerator and denominator of your fraction by (p^{2}  pr + r^{2}) to get a numerator of (I am going to use fractional exponents.)
and a denominator of
Now evaluate the limit of the fraction as x approaches zero. Penny
 


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