Thursday, 21 November 2013

limits - Is the derivative of a exponential function a^x always greater than the derivative of a polynomial x^n as x approaches infinity



with n and a being any constants > than 1.



I have tried taking the limxax/xn, and l'hopitals is telling me than xn can always be reduced to 1 with multiple iterations, so the limit is always infinity, and ax always grows faster than xn


Answer



Your argument using L'Hopilat rule is correct you need just to add the condition a>1



For a>1 it's true that ax is very larger then xn to see this you compose with a logarithm:

limxaxxn=limxexln(a)nln(x)=e+=+



because the linear functions are always larger than logarithmic functions.


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