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Calculus
Applications of Derivatives
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A plane is flying horizontally at an altitude of 1.9 kilometers with a velocity of 195 kilometers per hour when it flies over a radar station. Find the rate at which the distance is changing when the plane is 3.0 kilometers from the station. Round to the nearest tenth.


Drawing a diagram gives:
Identifing \(\displaystyle \frac{db}{dt}=195\), \(\displaystyle a=1.9\), and \(\displaystyle c=3.0\). Since the diagram is a right trinagle we can use the Pythagoren Theorem to get \(\displaystyle (1.9)^2 + b^2 = c^2\). Take the derivative with respect to time gives \(\displaystyle 0 + 2b\frac{db}{dt} = 2c\frac{dc}{dt}\). Solving for \(\displaystyle \frac{dc}{dt}\) gives \(\displaystyle \frac{dc}{dt} = \frac{b}{c}\frac{db}{dt}\)To find \(\displaystyle \frac{dc}{dt}\) we need to calculate \(\displaystyle b\) when \(\displaystyle c = 3.0\). Using the Pythagoren Theorem gives \(\displaystyle b = \sqrt{3.0^2 - 1.9^2}\). Finally calculating the value of the derivative \(\displaystyle \frac{dc}{dt}=\frac{ \sqrt{3.0^2 - 1.9^2} }{ 3.0 }\cdot 195 \approx 150.9\) kilometers per hour.

Download \(\LaTeX\)

\begin{question}A plane is flying horizontally at an altitude of 1.9 kilometers with a velocity of 195 kilometers per hour when it flies over a radar station. Find the rate at which the distance is changing when the plane is 3.0 kilometers from the station. Round to the nearest tenth. 
    \soln{9cm}{Drawing a diagram gives:\newline

\begin{center}
\begin{tikzpicture}
	 \draw(0, 0) -- (0, 3) node[midway, left]{a = 1.9 km};
	 \draw(0, 3) -- (5, 3) node[midway, above]{b};
	 \draw[dashed] (5, 3) -- (0, 0) node[midway, below]{c};
\end{tikzpicture}
\end{center}

Identifing $\frac{db}{dt}=195$, $a=1.9$, and $c=3.0$. Since the diagram is a right trinagle we can use the Pythagoren Theorem to get $(1.9)^2 + b^2 = c^2$. Take the derivative with respect to time gives $0 + 2b\frac{db}{dt} = 2c\frac{dc}{dt}$. Solving for $\frac{dc}{dt}$ gives $\frac{dc}{dt} = \frac{b}{c}\frac{db}{dt}$To find $\frac{dc}{dt}$ we need to calculate $b$ when $c = 3.0$. Using the Pythagoren Theorem gives $b = \sqrt{3.0^2 - 1.9^2}$. Finally calculating the value of the derivative $\frac{dc}{dt}=\frac{ \sqrt{3.0^2 - 1.9^2} }{ 3.0 }\cdot 195 \approx 150.9$ kilometers per hour.}

\end{question}

Download Question and Solution Environment\(\LaTeX\)
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\begin{document}\begin{question}(10pts) The question goes here!
    \soln{9cm}{The solution goes here.}

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HTML for Canvas
<p> <p>A plane is flying horizontally at an altitude of 1.9 kilometers with a velocity of 195 kilometers per hour when it flies over a radar station. Find the rate at which the distance is changing when the plane is 3.0 kilometers from the station. Round to the nearest tenth. </p> </p>
HTML for Canvas
<p> <p>Drawing a diagram gives:<br>
<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="612pt" height="792pt" viewBox="0 0 612 792" version="1.1">
<g id="surface1">
</g>
</svg>
Identifing  <img class="equation_image" title=" \displaystyle \frac{db}{dt}=195 " src="/equation_images/%20%5Cdisplaystyle%20%5Cfrac%7Bdb%7D%7Bdt%7D%3D195%20" alt="LaTeX:  \displaystyle \frac{db}{dt}=195 " data-equation-content=" \displaystyle \frac{db}{dt}=195 " /> ,  <img class="equation_image" title=" \displaystyle a=1.9 " src="/equation_images/%20%5Cdisplaystyle%20a%3D1.9%20" alt="LaTeX:  \displaystyle a=1.9 " data-equation-content=" \displaystyle a=1.9 " /> , and  <img class="equation_image" title=" \displaystyle c=3.0 " src="/equation_images/%20%5Cdisplaystyle%20c%3D3.0%20" alt="LaTeX:  \displaystyle c=3.0 " data-equation-content=" \displaystyle c=3.0 " /> . Since the diagram is a right trinagle we can use the Pythagoren Theorem to get  <img class="equation_image" title=" \displaystyle (1.9)^2 + b^2 = c^2 " src="/equation_images/%20%5Cdisplaystyle%20%281.9%29%5E2%20%2B%20b%5E2%20%3D%20c%5E2%20" alt="LaTeX:  \displaystyle (1.9)^2 + b^2 = c^2 " data-equation-content=" \displaystyle (1.9)^2 + b^2 = c^2 " /> . Take the derivative with respect to time gives  <img class="equation_image" title=" \displaystyle 0 + 2b\frac{db}{dt} = 2c\frac{dc}{dt} " src="/equation_images/%20%5Cdisplaystyle%200%20%2B%202b%5Cfrac%7Bdb%7D%7Bdt%7D%20%3D%202c%5Cfrac%7Bdc%7D%7Bdt%7D%20" alt="LaTeX:  \displaystyle 0 + 2b\frac{db}{dt} = 2c\frac{dc}{dt} " data-equation-content=" \displaystyle 0 + 2b\frac{db}{dt} = 2c\frac{dc}{dt} " /> . Solving for  <img class="equation_image" title=" \displaystyle \frac{dc}{dt} " src="/equation_images/%20%5Cdisplaystyle%20%5Cfrac%7Bdc%7D%7Bdt%7D%20" alt="LaTeX:  \displaystyle \frac{dc}{dt} " data-equation-content=" \displaystyle \frac{dc}{dt} " />  gives  <img class="equation_image" title=" \displaystyle \frac{dc}{dt} = \frac{b}{c}\frac{db}{dt} " src="/equation_images/%20%5Cdisplaystyle%20%5Cfrac%7Bdc%7D%7Bdt%7D%20%3D%20%5Cfrac%7Bb%7D%7Bc%7D%5Cfrac%7Bdb%7D%7Bdt%7D%20" alt="LaTeX:  \displaystyle \frac{dc}{dt} = \frac{b}{c}\frac{db}{dt} " data-equation-content=" \displaystyle \frac{dc}{dt} = \frac{b}{c}\frac{db}{dt} " /> To find  <img class="equation_image" title=" \displaystyle \frac{dc}{dt} " src="/equation_images/%20%5Cdisplaystyle%20%5Cfrac%7Bdc%7D%7Bdt%7D%20" alt="LaTeX:  \displaystyle \frac{dc}{dt} " data-equation-content=" \displaystyle \frac{dc}{dt} " />  we need to calculate  <img class="equation_image" title=" \displaystyle b " src="/equation_images/%20%5Cdisplaystyle%20b%20" alt="LaTeX:  \displaystyle b " data-equation-content=" \displaystyle b " />  when  <img class="equation_image" title=" \displaystyle c = 3.0 " src="/equation_images/%20%5Cdisplaystyle%20c%20%3D%203.0%20" alt="LaTeX:  \displaystyle c = 3.0 " data-equation-content=" \displaystyle c = 3.0 " /> . Using the Pythagoren Theorem gives  <img class="equation_image" title=" \displaystyle b = \sqrt{3.0^2 - 1.9^2} " src="/equation_images/%20%5Cdisplaystyle%20b%20%3D%20%5Csqrt%7B3.0%5E2%20-%201.9%5E2%7D%20" alt="LaTeX:  \displaystyle b = \sqrt{3.0^2 - 1.9^2} " data-equation-content=" \displaystyle b = \sqrt{3.0^2 - 1.9^2} " /> . Finally calculating the value of the derivative  <img class="equation_image" title=" \displaystyle \frac{dc}{dt}=\frac{ \sqrt{3.0^2 - 1.9^2} }{ 3.0 }\cdot 195 \approx 150.9 " src="/equation_images/%20%5Cdisplaystyle%20%5Cfrac%7Bdc%7D%7Bdt%7D%3D%5Cfrac%7B%20%5Csqrt%7B3.0%5E2%20-%201.9%5E2%7D%20%7D%7B%203.0%20%7D%5Ccdot%20195%20%5Capprox%20150.9%20" alt="LaTeX:  \displaystyle \frac{dc}{dt}=\frac{ \sqrt{3.0^2 - 1.9^2} }{ 3.0 }\cdot 195 \approx 150.9 " data-equation-content=" \displaystyle \frac{dc}{dt}=\frac{ \sqrt{3.0^2 - 1.9^2} }{ 3.0 }\cdot 195 \approx 150.9 " />  kilometers per hour.</p> </p>