I have two limits, to be solved by changing variables, that I'm having difficulty with:

lim x-> 1

x^(1/6) - 1

_________

x-1

I let x^(1/6) = u. When x -> 1, u -> 1, and made the denominator u^6 - 1. However, this still gives a denominator of 0, so I'm not sure if I subbed the values correctly, or if I'm just not seeing how this should be factored. The other one, which I'm unsure how to do, is:

lim x-> 1

x^(1/6) - 1

________

x^(1/3) - 1