Math  /  Calculus

QuestionFind the limit. limx(1+2x)172lnx\lim _{x \rightarrow \infty}(1+2 x)^{\frac{17}{2 \ln x}}

Studdy Solution

STEP 1

1. We are dealing with a limit as x x approaches infinity.
2. The expression involves both polynomial and logarithmic functions.
3. The limit may require the use of logarithmic properties and L'Hôpital's Rule.

STEP 2

1. Simplify the expression inside the limit.
2. Apply logarithmic transformation to simplify the exponent.
3. Use L'Hôpital's Rule if necessary.
4. Evaluate the limit.

STEP 3

First, consider the expression inside the limit:
limx(1+2x)172lnx \lim_{x \rightarrow \infty} (1 + 2x)^{\frac{17}{2 \ln x}}
To simplify, note that as x x \rightarrow \infty , 1+2x2x 1 + 2x \approx 2x . Thus, the expression becomes:
limx(2x)172lnx \lim_{x \rightarrow \infty} (2x)^{\frac{17}{2 \ln x}}

STEP 4

Apply a logarithmic transformation to the expression to simplify the exponent:
Let y=(2x)172lnx y = (2x)^{\frac{17}{2 \ln x}} .
Take the natural logarithm of both sides:
lny=172lnxln(2x) \ln y = \frac{17}{2 \ln x} \cdot \ln(2x)
lny=172lnx(ln2+lnx) \ln y = \frac{17}{2 \ln x} \cdot (\ln 2 + \ln x)

STEP 5

Simplify the expression:
lny=17(ln2+lnx)2lnx \ln y = \frac{17 (\ln 2 + \ln x)}{2 \ln x}
lny=17ln22lnx+17lnx2lnx \ln y = \frac{17 \ln 2}{2 \ln x} + \frac{17 \ln x}{2 \ln x}
lny=17ln22lnx+172 \ln y = \frac{17 \ln 2}{2 \ln x} + \frac{17}{2}
As x x \rightarrow \infty , the term 17ln22lnx0\frac{17 \ln 2}{2 \ln x} \rightarrow 0.
Thus,
lny172 \ln y \rightarrow \frac{17}{2}

STEP 6

Evaluate the limit:
Since lny172\ln y \rightarrow \frac{17}{2}, we have:
ye172 y \rightarrow e^{\frac{17}{2}}
Therefore, the limit is:
limx(1+2x)172lnx=e172 \lim_{x \rightarrow \infty} (1 + 2x)^{\frac{17}{2 \ln x}} = e^{\frac{17}{2}}
The value of the limit is:
e172 \boxed{e^{\frac{17}{2}}}

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