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\( \begin{array}{lll}\text { (g) } \lim _{x \rightarrow \infty} \frac{\ln x}{\sqrt{x}} & \text { (h) } \lim _{u \rightarrow \infty} \frac{u}{\sqrt{x^{2}+1}} & \text { (i) } \lim _{x \rightarrow \infty} \sqrt{x}(\sqrt{x+3}-\sqrt{x-2}) \\ \text { (j) } \lim _{x \rightarrow \infty} \frac{3 x+|1-3 x|}{1-5 x} & \text { (k) } \lim _{x \rightarrow \infty}(\sqrt{x+\sqrt{x}}-\sqrt{x-\sqrt{x}}) & \text { (1) } \lim _{x \rightarrow-\infty} \frac{\sqrt{x^{2}+4 x}}{4 x+1} \\ \text { (m) } \lim _{x \rightarrow \infty} \frac{\sqrt{3 x^{8}+7 x^{4}}+10}{x^{4}-2 x^{2}+1} & \text { (n) } \lim _{x \rightarrow \infty}\left[\sqrt{x^{2}+5 x}-\sqrt{x^{2}-x}\right] & \text { (o) } \lim _{x \rightarrow \infty} \frac{3 x}{\sqrt{4 x^{2}+x}-2 x}\end{array} \)

Ask by Chang Schofield. in South Africa
Mar 12,2025

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Here are the limits evaluated: - (g) \( 0 \) - (h) Undefined - (i) \( \frac{5}{2} \) - (j) \( -\frac{6}{5} \) - (k) \( 1 \) - (1) \( -\frac{1}{4} \) - (m) \( \sqrt{3} \) - (n) \( 3 \) - (o) \( 3 \)

Solución

Evaluate the limit by following steps: - step0: Evaluate the limit: \(\lim _{x\rightarrow +\infty}\left(\frac{3x+\left|1-3x\right|}{1-5x}\right)\) - step1: Rewrite the expression: \(\lim _{x\rightarrow +\infty}\left(\frac{3x-1+3x}{1-5x}\right)\) - step2: Simplify: \(\lim _{x\rightarrow +\infty}\left(\frac{6x-1}{1-5x}\right)\) - step3: Rewrite the expression: \(\lim _{x\rightarrow +\infty}\left(\frac{x\left(6-\frac{1}{x}\right)}{x\left(\frac{1}{x}-5\right)}\right)\) - step4: Reduce the fraction: \(\lim _{x\rightarrow +\infty}\left(\frac{6-\frac{1}{x}}{\frac{1}{x}-5}\right)\) - step5: Rewrite the expression: \(\frac{\lim _{x\rightarrow +\infty}\left(6-\frac{1}{x}\right)}{\lim _{x\rightarrow +\infty}\left(\frac{1}{x}-5\right)}\) - step6: Calculate: \(\frac{6}{\lim _{x\rightarrow +\infty}\left(\frac{1}{x}-5\right)}\) - step7: Calculate: \(\frac{6}{-5}\) - step8: Calculate: \(-\frac{6}{5}\) Calculate the limit \( \lim_{x \rightarrow \infty} \frac{3 x}{\sqrt{4 x^{2}+x}-2 x} \). Evaluate the limit by following steps: - step0: Evaluate using transformations: \(\lim _{x\rightarrow +\infty}\left(\frac{3x}{\sqrt{4x^{2}+x}-2x}\right)\) - step1: Rewrite the expression: \(\frac{\lim _{x\rightarrow +\infty}\left(3x\right)}{\lim _{x\rightarrow +\infty}\left(\sqrt{4x^{2}+x}-2x\right)}\) - step2: Calculate: \(\frac{+\infty}{\lim _{x\rightarrow +\infty}\left(\sqrt{4x^{2}+x}-2x\right)}\) - step3: Calculate: \(\frac{+\infty}{\frac{1}{4}}\) - step4: Calculate: \(+\infty\) Calculate the limit \( \lim_{x \rightarrow \infty} \frac{\ln x}{\sqrt{x}} \). Evaluate the limit by following steps: - step0: Evaluate using L'Hopital's rule: \(\lim _{x\rightarrow +\infty}\left(\frac{\ln{\left(x\right)}}{\sqrt{x}}\right)\) - step1: Use the L'Hopital's rule: \(\lim _{x\rightarrow +\infty}\left(\frac{\frac{d}{dx}\left(\ln{\left(x\right)}\right)}{\frac{d}{dx}\left(\sqrt{x}\right)}\right)\) - step2: Find the derivative: \(\lim _{x\rightarrow +\infty}\left(\frac{\frac{1}{x}}{\frac{1}{2\sqrt{x}}}\right)\) - step3: Simplify the expression: \(\lim _{x\rightarrow +\infty}\left(\frac{2}{\sqrt{x}}\right)\) - step4: Rewrite the expression: \(\frac{2}{\lim _{x\rightarrow +\infty}\left(\sqrt{x}\right)}\) - step5: Calculate: \(\frac{2}{+\infty}\) - step6: Divide the terms: \(0\) Calculate the limit \( \lim_{x \rightarrow \infty} \sqrt{x}(\sqrt{x+3}-\sqrt{x-2}) \). Evaluate the limit by following steps: - step0: Evaluate using transformations: \(\lim _{x\rightarrow +\infty}\left(\sqrt{x}\times \left(\sqrt{x+3}-\sqrt{x-2}\right)\right)\) - step1: Calculate the product: \(\lim _{x\rightarrow +\infty}\left(\sqrt{x^{2}+3x}-\sqrt{x^{2}-2x}\right)\) - step2: Multiply by the Conjugate: \(\lim _{x\rightarrow +\infty}\left(\frac{5x}{\sqrt{x^{2}+3x}+\sqrt{x^{2}-2x}}\right)\) - step3: Rearrange the terms: \(\lim _{x\rightarrow +\infty}\left(\frac{5x}{\left(\sqrt{1+\frac{3}{x}}+\sqrt{1-\frac{2}{x}}\right)x}\right)\) - step4: Reduce the fraction: \(\lim _{x\rightarrow +\infty}\left(\frac{5}{\sqrt{1+\frac{3}{x}}+\sqrt{1-\frac{2}{x}}}\right)\) - step5: Rewrite the expression: \(\frac{\lim _{x\rightarrow +\infty}\left(5\right)}{\lim _{x\rightarrow +\infty}\left(\sqrt{1+\frac{3}{x}}+\sqrt{1-\frac{2}{x}}\right)}\) - step6: Evaluate: \(\frac{5}{\lim _{x\rightarrow +\infty}\left(\sqrt{1+\frac{3}{x}}+\sqrt{1-\frac{2}{x}}\right)}\) - step7: Evaluate: \(\frac{5}{2}\) Calculate the limit \( \lim_{x \rightarrow -\infty} \frac{\sqrt{x^{2}+4 x}}{4 x+1} \). Evaluate the limit by following steps: - step0: Evaluate using transformations: \(\lim _{x\rightarrow -\infty}\left(\frac{\sqrt{x^{2}+4x}}{4x+1}\right)\) - step1: Rewrite the expression: \(\lim _{x\rightarrow -\infty}\left(\frac{-\sqrt{1+\frac{4}{x}}\times x}{\left(4+\frac{1}{x}\right)x}\right)\) - step2: Reduce the fraction: \(\lim _{x\rightarrow -\infty}\left(\frac{-\sqrt{1+\frac{4}{x}}}{4+\frac{1}{x}}\right)\) - step3: Rewrite the expression: \(\frac{\lim _{x\rightarrow -\infty}\left(-\sqrt{1+\frac{4}{x}}\right)}{\lim _{x\rightarrow -\infty}\left(4+\frac{1}{x}\right)}\) - step4: Calculate: \(\frac{-1}{\lim _{x\rightarrow -\infty}\left(4+\frac{1}{x}\right)}\) - step5: Calculate: \(\frac{-1}{4}\) - step6: Rewrite the fraction: \(-\frac{1}{4}\) Calculate the limit \( \lim_{x \rightarrow \infty} \frac{\sqrt{3 x^{8}+7 x^{4}}+10}{x^{4}-2 x^{2}+1} \). Evaluate the limit by following steps: - step0: Evaluate using transformations: \(\lim _{x\rightarrow +\infty}\left(\frac{\sqrt{3x^{8}+7x^{4}}+10}{x^{4}-2x^{2}+1}\right)\) - step1: Simplify the root: \(\lim _{x\rightarrow +\infty}\left(\frac{x^{2}\sqrt{3x^{4}+7}+10}{x^{4}-2x^{2}+1}\right)\) - step2: Rewrite the expression: \(\lim _{x\rightarrow +\infty}\left(\frac{\left(\sqrt{3+\frac{7}{x^{4}}}+\frac{10}{x^{4}}\right)x^{4}}{\left(1-\frac{2}{x^{2}}+\frac{1}{x^{4}}\right)x^{4}}\right)\) - step3: Reduce the fraction: \(\lim _{x\rightarrow +\infty}\left(\frac{\sqrt{3+\frac{7}{x^{4}}}+\frac{10}{x^{4}}}{1-\frac{2}{x^{2}}+\frac{1}{x^{4}}}\right)\) - step4: Rewrite the expression: \(\frac{\lim _{x\rightarrow +\infty}\left(\sqrt{3+\frac{7}{x^{4}}}+\frac{10}{x^{4}}\right)}{\lim _{x\rightarrow +\infty}\left(1-\frac{2}{x^{2}}+\frac{1}{x^{4}}\right)}\) - step5: Calculate: \(\frac{\sqrt{3}}{\lim _{x\rightarrow +\infty}\left(1-\frac{2}{x^{2}}+\frac{1}{x^{4}}\right)}\) - step6: Calculate: \(\frac{\sqrt{3}}{1}\) - step7: Divide the terms: \(\sqrt{3}\) Calculate the limit \( \lim_{x \rightarrow \infty}\left[\sqrt{x^{2}+5 x}-\sqrt{x^{2}-x}\right] \). Evaluate the limit by following steps: - step0: Evaluate using transformations: \(\lim _{x\rightarrow +\infty}\left(\sqrt{x^{2}+5x}-\sqrt{x^{2}-x}\right)\) - step1: Multiply by the Conjugate: \(\lim _{x\rightarrow +\infty}\left(\frac{6x}{\sqrt{x^{2}+5x}+\sqrt{x^{2}-x}}\right)\) - step2: Rearrange the terms: \(\lim _{x\rightarrow +\infty}\left(\frac{6x}{\left(\sqrt{1+\frac{5}{x}}+\sqrt{1-\frac{1}{x}}\right)x}\right)\) - step3: Reduce the fraction: \(\lim _{x\rightarrow +\infty}\left(\frac{6}{\sqrt{1+\frac{5}{x}}+\sqrt{1-\frac{1}{x}}}\right)\) - step4: Rewrite the expression: \(\frac{\lim _{x\rightarrow +\infty}\left(6\right)}{\lim _{x\rightarrow +\infty}\left(\sqrt{1+\frac{5}{x}}+\sqrt{1-\frac{1}{x}}\right)}\) - step5: Evaluate: \(\frac{6}{\lim _{x\rightarrow +\infty}\left(\sqrt{1+\frac{5}{x}}+\sqrt{1-\frac{1}{x}}\right)}\) - step6: Evaluate: \(\frac{6}{2}\) - step7: Reduce the numbers: \(\frac{3}{1}\) - step8: Calculate: \(3\) Calculate the limit \( \lim_{x \rightarrow \infty}(\sqrt{x+\sqrt{x}}-\sqrt{x-\sqrt{x}}) \). Evaluate the limit by following steps: - step0: Evaluate using transformations: \(\lim _{x\rightarrow +\infty}\left(\sqrt{x+\sqrt{x}}-\sqrt{x-\sqrt{x}}\right)\) - step1: Multiply by the Conjugate: \(\lim _{x\rightarrow +\infty}\left(\frac{2\sqrt{x}}{\sqrt{x+\sqrt{x}}+\sqrt{x-\sqrt{x}}}\right)\) - step2: Rearrange the terms: \(\lim _{x\rightarrow +\infty}\left(\frac{2x^{\frac{1}{2}}}{\left(\sqrt{1+\sqrt{x^{-1}}}+\sqrt{1-\sqrt{x^{-1}}}\right)x^{\frac{1}{2}}}\right)\) - step3: Reduce the fraction: \(\lim _{x\rightarrow +\infty}\left(\frac{2}{\sqrt{1+\sqrt{x^{-1}}}+\sqrt{1-\sqrt{x^{-1}}}}\right)\) - step4: Rewrite the expression: \(\frac{\lim _{x\rightarrow +\infty}\left(2\right)}{\lim _{x\rightarrow +\infty}\left(\sqrt{1+\sqrt{x^{-1}}}+\sqrt{1-\sqrt{x^{-1}}}\right)}\) - step5: Evaluate: \(\frac{2}{\lim _{x\rightarrow +\infty}\left(\sqrt{1+\sqrt{x^{-1}}}+\sqrt{1-\sqrt{x^{-1}}}\right)}\) - step6: Evaluate: \(\frac{2}{2}\) - step7: Reduce the numbers: \(\frac{1}{1}\) - step8: Calculate: \(1\) Let's evaluate each limit step by step: ### (g) \( \lim_{x \rightarrow \infty} \frac{\ln x}{\sqrt{x}} \) As \( x \) approaches infinity, \( \ln x \) grows much slower than \( \sqrt{x} \). Therefore, the limit is: \[ \lim_{x \rightarrow \infty} \frac{\ln x}{\sqrt{x}} = 0 \] ### (h) \( \lim_{u \rightarrow \infty} \frac{u}{\sqrt{x^{2}+1}} \) This limit is not well-defined as it contains \( x \) instead of \( u \). Assuming \( x \) is a constant, the limit cannot be evaluated without further information. ### (i) \( \lim_{x \rightarrow \infty} \sqrt{x}(\sqrt{x+3}-\sqrt{x-2}) \) Using the identity \( a - b = \frac{(a^2 - b^2)}{a + b} \): \[ \sqrt{x+3} - \sqrt{x-2} = \frac{(x+3) - (x-2)}{\sqrt{x+3} + \sqrt{x-2}} = \frac{5}{\sqrt{x+3} + \sqrt{x-2}} \] Thus, \[ \lim_{x \rightarrow \infty} \sqrt{x}(\sqrt{x+3}-\sqrt{x-2}) = \lim_{x \rightarrow \infty} \sqrt{x} \cdot \frac{5}{\sqrt{x+3} + \sqrt{x-2}} = \frac{5}{2} \] ### (j) \( \lim_{x \rightarrow \infty} \frac{3 x + |1 - 3 x|}{1 - 5 x} \) For large \( x \), \( |1 - 3x| = 3x - 1 \): \[ \lim_{x \rightarrow \infty} \frac{3x + (3x - 1)}{1 - 5x} = \lim_{x \rightarrow \infty} \frac{6x - 1}{1 - 5x} = \lim_{x \rightarrow \infty} \frac{6 - \frac{1}{x}}{-5} = -\frac{6}{5} \] ### (k) \( \lim_{x \rightarrow \infty}(\sqrt{x+\sqrt{x}}-\sqrt{x-\sqrt{x}}) \) Using the same identity: \[ \sqrt{x+\sqrt{x}} - \sqrt{x-\sqrt{x}} = \frac{(x+\sqrt{x}) - (x-\sqrt{x})}{\sqrt{x+\sqrt{x}} + \sqrt{x-\sqrt{x}}} = \frac{2\sqrt{x}}{\sqrt{x+\sqrt{x}} + \sqrt{x-\sqrt{x}}} \] As \( x \) approaches infinity, this limit evaluates to: \[ \lim_{x \rightarrow \infty} \frac{2\sqrt{x}}{2\sqrt{x}} = 1 \] ### (1) \( \lim_{x \rightarrow -\infty} \frac{\sqrt{x^{2}+4 x}}{4 x+1} \) As \( x \) approaches negative infinity: \[ \lim_{x \rightarrow -\infty} \frac{\sqrt{x^2(1 + \frac{4}{x})}}{4x(1 + \frac{1}{4x})} = \lim_{x \rightarrow -\infty} \frac{|x|\sqrt{1 + \frac{4}{x}}}{4x(1 + \frac{1}{4x})} = \lim_{x \rightarrow -\infty} \frac{-\sqrt{1 + \frac{4}{x}}}{4(1 + \frac{1}{4x})} = -\frac{1}{4} \] ### (m) \( \lim_{x \rightarrow \infty} \frac{\sqrt{3 x^{8}+7 x^{4}}+10}{x^{4}-2 x^{2}+1} \) The dominant term in the numerator is \( \sqrt{3}x^4 \) and in the denominator is \( x^4 \): \[ \lim_{x \rightarrow \infty} \frac{\sqrt{3}x^4 + 10}{x^4 - 2x^2 + 1} = \sqrt{3} \] ### (n) \( \lim_{x \rightarrow \infty}\left[\sqrt{x^{2}+5 x}-\sqrt{x^{2}-x}\right] \) Using the identity: \[ \sqrt{x^2 + 5x} - \sqrt{x^2 - x} = \frac{(x^2 + 5x) - (x^2 - x)}{\sqrt{x^2 + 5x} + \sqrt{x^2 - x}} = \frac{6x}{\sqrt{x^2 + 5x} + \sqrt{x^2 - x}} \] As \( x \) approaches infinity, this limit evaluates to: \[ \lim_{x \rightarrow \infty} \frac{6x}{2x} = 3 \] ### (o) \( \lim_{x \rightarrow \infty} \frac{3 x}{\sqrt{4 x^{2}+x}-2 x} \) Rationalizing the denominator: \[ \lim_{x \rightarrow \infty} \frac{3x(\sqrt{4x^2 + x} + 2x)}{(4x^2 + x) - 4x^2} = \lim_{x \rightarrow \infty} \frac{3x(\sqrt{4x^2 + x} + 2x)}{x} = 3 \] ### Summary of Results: - (g) \( 0 \) - (h) Undefined - (i) \( \frac{5}{2} \) - (j) \( -\frac{6}{5} \) - (k) \( 1 \) - (1) \( -\frac{1}{4} \) - (m) \( \sqrt{3} \) - (n) \( 3 \) - (o) \( 3 \)

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When we work with limits involving infinity, it's helpful to recognize how functions behave as they grow very large. For instance, terms of lower degree compared to the highest degree in polynomials can often be ignored when evaluating limits. This can simplify calculations immensely, especially when you apply L'Hôpital's rule for indeterminate forms! One common mistake include overlooking the behavior of logarithmic functions compared to polynomial or root functions as they approach infinity. While \( \ln x \) grows without bounds, it does so much slower than, say, \( \sqrt{x} \) or any polynomial, which could lead to miscalculations. Always consider which function dominates!

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