Math  /  Calculus

Questionlimxln(x2+1)ln(3x2+7)\lim _{x \rightarrow \infty} \frac{\ln \left(x^{2}+1\right)}{\ln \left(3 x^{2}+7\right)}

Studdy Solution

STEP 1

1. We are dealing with a limit as x x approaches infinity.
2. Both the numerator and the denominator are logarithmic functions.
3. We will use properties of logarithms and limits to simplify the expression.

STEP 2

1. Simplify the logarithmic expressions.
2. Apply properties of limits.
3. Evaluate the limit.

STEP 3

First, simplify the logarithmic expressions using properties of logarithms. Recall that ln(ab)=lna+lnb\ln(a \cdot b) = \ln a + \ln b and ln(ab)=blna\ln(a^b) = b \ln a.
For the numerator: ln(x2+1) \ln(x^2 + 1)
For the denominator: ln(3x2+7) \ln(3x^2 + 7)
Both expressions can be simplified by focusing on the dominant term as x x \to \infty .

STEP 4

As x x \to \infty , the dominant term in both x2+1 x^2 + 1 and 3x2+7 3x^2 + 7 is the x2 x^2 term. Thus, we approximate:
ln(x2+1)ln(x2)=2ln(x) \ln(x^2 + 1) \approx \ln(x^2) = 2\ln(x)
ln(3x2+7)ln(3x2)=ln(3)+2ln(x) \ln(3x^2 + 7) \approx \ln(3x^2) = \ln(3) + 2\ln(x)

STEP 5

Substitute the approximations back into the original limit expression:
limxln(x2+1)ln(3x2+7)limx2ln(x)ln(3)+2ln(x) \lim_{x \to \infty} \frac{\ln(x^2 + 1)}{\ln(3x^2 + 7)} \approx \lim_{x \to \infty} \frac{2\ln(x)}{\ln(3) + 2\ln(x)}
Factor out 2ln(x) 2\ln(x) from the denominator:
=limx2ln(x)2ln(x)(1+ln(3)2ln(x)) = \lim_{x \to \infty} \frac{2\ln(x)}{2\ln(x)(1 + \frac{\ln(3)}{2\ln(x)})}
Simplify the expression:
=limx22(1+ln(3)2ln(x)) = \lim_{x \to \infty} \frac{2}{2(1 + \frac{\ln(3)}{2\ln(x)})}
=limx11+ln(3)2ln(x) = \lim_{x \to \infty} \frac{1}{1 + \frac{\ln(3)}{2\ln(x)}}

STEP 6

As x x \to \infty , ln(x)\ln(x) \to \infty, so ln(3)2ln(x)0\frac{\ln(3)}{2\ln(x)} \to 0.
Thus, the limit becomes:
limx11+0=1 \lim_{x \to \infty} \frac{1}{1 + 0} = 1
The value of the limit is:
1 \boxed{1}

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