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Calculus
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Evaluate the limit \(\displaystyle \displaystyle\lim_{x \to -\infty}\left(6 x + \sqrt{36 x^{2} - 10 x + 14}\right)\)


Building the fraction by muliplying by the conjuate gives: \(\displaystyle \lim_{x\to-\infty}\frac{6 x + \sqrt{36 x^{2} - 10 x + 14}}{1}\cdot\left(\frac{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}\right)\) Simplifying gives \(\displaystyle \lim_{x \to -\infty} \frac{14 - 10 x}{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}\)factoring an \(\displaystyle x^2\) out of the radical in the denomiator and using the fact that \(\displaystyle \sqrt{x^2}=|x|\) gives \(\displaystyle \lim_{x \to -\infty} \frac{x \left(-10 + \frac{14}{x}\right)}{- 6 x + \sqrt{36 - \frac{10}{x} + \frac{14}{x^{2}}} \left|{x}\right|}\) Using the fact that \(\displaystyle |x| =-x\) when \(\displaystyle x<0\) and reducing gives \(\displaystyle \lim_{x \to -\infty}\left(\frac{-10 + \frac{14}{x}}{- \sqrt{36 - \frac{10}{x} + \frac{14}{x^{2}}} - 6}\right) = \frac{5}{6}\)

Download \(\LaTeX\)

\begin{question}Evaluate the limit $\displaystyle\lim_{x \to -\infty}\left(6 x + \sqrt{36 x^{2} - 10 x + 14}\right)$
    \soln{9cm}{Building the fraction by muliplying by the conjuate gives: $\lim_{x\to-\infty}\frac{6 x + \sqrt{36 x^{2} - 10 x + 14}}{1}\cdot\left(\frac{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}\right)$ Simplifying gives $\lim_{x \to -\infty} \frac{14 - 10 x}{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}$factoring an $x^2$ out of the radical in the denomiator and using the fact that $\sqrt{x^2}=|x|$ gives $\lim_{x \to -\infty} \frac{x \left(-10 + \frac{14}{x}\right)}{- 6 x + \sqrt{36 - \frac{10}{x} + \frac{14}{x^{2}}} \left|{x}\right|}$ Using the fact that $|x| =-x$ when $x<0$ and reducing gives $\lim_{x \to -\infty}\left(\frac{-10 + \frac{14}{x}}{- \sqrt{36 - \frac{10}{x} + \frac{14}{x^{2}}} - 6}\right) = \frac{5}{6}$ }

\end{question}

Download Question and Solution Environment\(\LaTeX\)
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HTML for Canvas
<p> <p>Evaluate the limit  <img class="equation_image" title=" \displaystyle \displaystyle\lim_{x \to -\infty}\left(6 x + \sqrt{36 x^{2} - 10 x + 14}\right) " src="/equation_images/%20%5Cdisplaystyle%20%5Cdisplaystyle%5Clim_%7Bx%20%5Cto%20-%5Cinfty%7D%5Cleft%286%20x%20%2B%20%5Csqrt%7B36%20x%5E%7B2%7D%20-%2010%20x%20%2B%2014%7D%5Cright%29%20" alt="LaTeX:  \displaystyle \displaystyle\lim_{x \to -\infty}\left(6 x + \sqrt{36 x^{2} - 10 x + 14}\right) " data-equation-content=" \displaystyle \displaystyle\lim_{x \to -\infty}\left(6 x + \sqrt{36 x^{2} - 10 x + 14}\right) " /> </p> </p>
HTML for Canvas
<p> <p>Building the fraction by muliplying by the conjuate gives:  <img class="equation_image" title=" \displaystyle \lim_{x\to-\infty}\frac{6 x + \sqrt{36 x^{2} - 10 x + 14}}{1}\cdot\left(\frac{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}\right) " src="/equation_images/%20%5Cdisplaystyle%20%5Clim_%7Bx%5Cto-%5Cinfty%7D%5Cfrac%7B6%20x%20%2B%20%5Csqrt%7B36%20x%5E%7B2%7D%20-%2010%20x%20%2B%2014%7D%7D%7B1%7D%5Ccdot%5Cleft%28%5Cfrac%7B-%206%20x%20%2B%20%5Csqrt%7B36%20x%5E%7B2%7D%20-%2010%20x%20%2B%2014%7D%7D%7B-%206%20x%20%2B%20%5Csqrt%7B36%20x%5E%7B2%7D%20-%2010%20x%20%2B%2014%7D%7D%5Cright%29%20" alt="LaTeX:  \displaystyle \lim_{x\to-\infty}\frac{6 x + \sqrt{36 x^{2} - 10 x + 14}}{1}\cdot\left(\frac{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}\right) " data-equation-content=" \displaystyle \lim_{x\to-\infty}\frac{6 x + \sqrt{36 x^{2} - 10 x + 14}}{1}\cdot\left(\frac{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}{- 6 x + \sqrt{36 x^{2} - 10 x + 14}}\right) " />  Simplifying gives  <img class="equation_image" title=" \displaystyle \lim_{x \to -\infty} \frac{14 - 10 x}{- 6 x + \sqrt{36 x^{2} - 10 x + 14}} " src="/equation_images/%20%5Cdisplaystyle%20%5Clim_%7Bx%20%5Cto%20-%5Cinfty%7D%20%5Cfrac%7B14%20-%2010%20x%7D%7B-%206%20x%20%2B%20%5Csqrt%7B36%20x%5E%7B2%7D%20-%2010%20x%20%2B%2014%7D%7D%20" alt="LaTeX:  \displaystyle \lim_{x \to -\infty} \frac{14 - 10 x}{- 6 x + \sqrt{36 x^{2} - 10 x + 14}} " data-equation-content=" \displaystyle \lim_{x \to -\infty} \frac{14 - 10 x}{- 6 x + \sqrt{36 x^{2} - 10 x + 14}} " /> factoring an  <img class="equation_image" title=" \displaystyle x^2 " src="/equation_images/%20%5Cdisplaystyle%20x%5E2%20" alt="LaTeX:  \displaystyle x^2 " data-equation-content=" \displaystyle x^2 " />  out of the radical in the denomiator and using the fact that  <img class="equation_image" title=" \displaystyle \sqrt{x^2}=|x| " src="/equation_images/%20%5Cdisplaystyle%20%5Csqrt%7Bx%5E2%7D%3D%7Cx%7C%20" alt="LaTeX:  \displaystyle \sqrt{x^2}=|x| " data-equation-content=" \displaystyle \sqrt{x^2}=|x| " />  gives  <img class="equation_image" title=" \displaystyle \lim_{x \to -\infty} \frac{x \left(-10 + \frac{14}{x}\right)}{- 6 x + \sqrt{36 - \frac{10}{x} + \frac{14}{x^{2}}} \left|{x}\right|} " src="/equation_images/%20%5Cdisplaystyle%20%5Clim_%7Bx%20%5Cto%20-%5Cinfty%7D%20%5Cfrac%7Bx%20%5Cleft%28-10%20%2B%20%5Cfrac%7B14%7D%7Bx%7D%5Cright%29%7D%7B-%206%20x%20%2B%20%5Csqrt%7B36%20-%20%5Cfrac%7B10%7D%7Bx%7D%20%2B%20%5Cfrac%7B14%7D%7Bx%5E%7B2%7D%7D%7D%20%5Cleft%7C%7Bx%7D%5Cright%7C%7D%20" alt="LaTeX:  \displaystyle \lim_{x \to -\infty} \frac{x \left(-10 + \frac{14}{x}\right)}{- 6 x + \sqrt{36 - \frac{10}{x} + \frac{14}{x^{2}}} \left|{x}\right|} " data-equation-content=" \displaystyle \lim_{x \to -\infty} \frac{x \left(-10 + \frac{14}{x}\right)}{- 6 x + \sqrt{36 - \frac{10}{x} + \frac{14}{x^{2}}} \left|{x}\right|} " />  Using the fact that  <img class="equation_image" title=" \displaystyle |x| =-x " src="/equation_images/%20%5Cdisplaystyle%20%7Cx%7C%20%3D-x%20" alt="LaTeX:  \displaystyle |x| =-x " data-equation-content=" \displaystyle |x| =-x " />  when  <img class="equation_image" title=" \displaystyle x<0 " src="/equation_images/%20%5Cdisplaystyle%20x%3C0%20" alt="LaTeX:  \displaystyle x<0 " data-equation-content=" \displaystyle x<0 " />  and reducing gives  <img class="equation_image" title=" \displaystyle \lim_{x \to -\infty}\left(\frac{-10 + \frac{14}{x}}{- \sqrt{36 - \frac{10}{x} + \frac{14}{x^{2}}} - 6}\right) = \frac{5}{6} " src="/equation_images/%20%5Cdisplaystyle%20%5Clim_%7Bx%20%5Cto%20-%5Cinfty%7D%5Cleft%28%5Cfrac%7B-10%20%2B%20%5Cfrac%7B14%7D%7Bx%7D%7D%7B-%20%5Csqrt%7B36%20-%20%5Cfrac%7B10%7D%7Bx%7D%20%2B%20%5Cfrac%7B14%7D%7Bx%5E%7B2%7D%7D%7D%20-%206%7D%5Cright%29%20%3D%20%5Cfrac%7B5%7D%7B6%7D%20" alt="LaTeX:  \displaystyle \lim_{x \to -\infty}\left(\frac{-10 + \frac{14}{x}}{- \sqrt{36 - \frac{10}{x} + \frac{14}{x^{2}}} - 6}\right) = \frac{5}{6} " data-equation-content=" \displaystyle \lim_{x \to -\infty}\left(\frac{-10 + \frac{14}{x}}{- \sqrt{36 - \frac{10}{x} + \frac{14}{x^{2}}} - 6}\right) = \frac{5}{6} " />  </p> </p>