Question

\( \lim _{x \rightarrow 1} (\frac{x}{x-1}-\frac{1}{lnx}) \)

Ask by Gardner Rogers. in Bangladesh
Mar 10,2025

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Answer

The limit is 0.5.

Solution

Calculate the limit \( \lim_{x\rightarrow 1} (\frac{x}{x-1}-\frac{1}{\ln(x)}) \). Evaluate the limit by following steps: - step0: Evaluate using L'Hopital's rule: \(\lim _{x\rightarrow 1}\left(\frac{x}{x-1}-\frac{1}{\ln{\left(x\right)}}\right)\) - step1: Transform the expression: \(\lim _{x\rightarrow 1}\left(\frac{x\ln{\left(x\right)}-x+1}{\left(x-1\right)\times \ln{\left(x\right)}}\right)\) - step2: Use the L'Hopital's rule: \(\lim _{x\rightarrow 1}\left(\frac{\frac{d}{dx}\left(x\ln{\left(x\right)}-x+1\right)}{\frac{d}{dx}\left(\left(x-1\right)\times \ln{\left(x\right)}\right)}\right)\) - step3: Find the derivative: \(\lim _{x\rightarrow 1}\left(\frac{\ln{\left(x\right)}}{\frac{\ln{\left(x\right)}\times x+x-1}{x}}\right)\) - step4: Simplify the expression: \(\lim _{x\rightarrow 1}\left(\frac{1}{1+\frac{1}{\ln{\left(x\right)}}-\frac{1}{x\ln{\left(x\right)}}}\right)\) - step5: Rewrite the expression: \(\frac{1}{\lim _{x\rightarrow 1}\left(1+\frac{1}{\ln{\left(x\right)}}-\frac{1}{x\ln{\left(x\right)}}\right)}\) - step6: Calculate: \(\frac{1}{2}\) The limit of the expression \( \frac{x}{x-1}-\frac{1}{\ln(x)} \) as \( x \) approaches 1 is \( \frac{1}{2} \) or 0.5.

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To evaluate the limit \( \lim _{x \rightarrow 1} \left(\frac{x}{x-1}-\frac{1}{\ln x}\right) \), we start by noticing that both terms approach infinity as \( x \) approaches 1. Hence, we can rewrite the expression with a common denominator: \[ \frac{x \ln x - (x - 1)}{(x - 1) \ln x} \] Now, we can simplify the numerator: \[ x \ln x - x + 1 \] Next, to handle the limit, we can apply L'Hôpital's rule since we have an indeterminate form \( \frac{0}{0} \) as \( x \rightarrow 1 \). We differentiate the numerator and the denominator separately. For the numerator \( x \ln x - x + 1 \): - The derivative is \( \ln x + 1 - 1 = \ln x \). For the denominator \( (x - 1) \ln x \): - Using the product rule: \( (x - 1) \cdot \frac{1}{x} + \ln x \). Applying L'Hôpital's Rule, we compute the limit as \( x \to 1 \): \[ \lim_{x \to 1} \frac{\ln x}{(x - 1) \cdot \frac{1}{x} + \ln x} \] At \( x = 1 \), \( \ln 1 = 0 \), which gives us the \( \frac{0}{0} \) form again. We apply L'Hôpital's rule a second time. For the numerator: - The derivative of \( \ln x \) is \( \frac{1}{x} \). For the denominator: - Derivative of \( (x - 1) \cdot \frac{1}{x} + \ln x \): - The derivative of the first part is \( \frac{1}{x} - \frac{x-1}{x^2} \) and \( \frac{1}{x} \). - Combining yields: \( \frac{1}{x} - \frac{1}{x} + \frac{1}{x^2} = \frac{1}{x^2} \). So, applying L'Hôpital's rule again, we have: \[ \lim_{x \to 1} \frac{\frac{1}{x}}{\frac{1}{x^2}} = \lim_{x \to 1} x = 1. \] Therefore, the limit is \[ \boxed{1}. \]

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