Ok as sqrt(x^6 + 5) approaches infinity it goes to x^3 Same with the denominator because x^3 is the highest power
On the bottom, the factor on x^3 is 4 so on the top to make the limit evaluate to 1/3, a has to be 16/9 so then when you neglect all of the other powers besides the highest, it goes to 4/3 because you take the square root and then it simplifies to 1/3
