Tuesday, September 23, 2014

Evaluate the limit of the function (x^x- 1)/(x-1), if x goes to 1 but do not use L'Hospital's theorem.

Let f(x) = x^x


If we'll put x
= 1 => f(1) = 1^1  =1


We'll re-write the function
whose limit has to be found out:


lim (f(x) - 1)/(x -
1)


By definition, the derivative of a function f(x), at the
point x = 1 is: lim (f(x) - 1)/(x - 1) = f'(1).


We'll have
to determine the expression of the 1st derivative of
f(x).


We'll take natural logarithms both
sides:


ln f(x) = ln (x^x)


ln
f(x) = x*ln x


We'll differentiate with respect to x both
sides:


f'(x)/f(x) = ln x +
x/x


f'(x)/f(x) = ln x +
1


f'(x) = f(x)*(ln x +
1)


f'(x) = (x^x)*(ln x +
1)


Now, we'll replace x by
1:


f'(1) = 1*(ln 1 + 1)


f'(1)
= 1


Therefore, the limit of the function,
when x approaches to 1, is lim (x^x - 1)/(x - 1) =
1.

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