Suppose that a tangent line is drawn to the hyperbola $xy = c$ at a point $P$.
a.) Prove that the midpoint of the line segment cut from this tangent line lay the coordinate axes is $P$.
b.) Prove that the triangle formed by the tangent line and the coordinate axes always has the same area, no
matter where $P$ is located on the hyperbola.
$
\begin{equation}
\begin{aligned}
\text{a.) since } xy &= c,\\
y &= \frac{c}{x}\\
\frac{dy}{dx} &= c \frac{d}{dx}\left(\frac{1}{x}\right)\\
\frac{dy}{dx} &= c \left(\frac{-1}{x^2}\right)\\
\frac{dy}{dx} &= -\frac{c}{x^2}
\end{aligned}
\end{equation}
$
Now we can get the tangent line through $\displaystyle P \left(x_1, \frac{c}{x}\right)$ by using point slope form.
$
\begin{equation}
\begin{aligned}
y -y_1 &= m(x-x_1)\\
y - \left(\frac{c}{x_1}\right) &= \frac{-c}{x_1^2}(x-x_1)\\
y-\frac{c}{x_1} &= \frac{-c}{x_1^2} x + \frac{c}{x_1}\\
y &= \frac{-c}{x_1^2} + \frac{2c}{x_1}
\end{aligned}
\end{equation}
$
Notice that the $y$-intercept $\displaystyle \frac{2c}{x_1}$ is twice the $y$-coordinate of $P$.
Solving for $x$-intercept,
$
\begin{equation}
\begin{aligned}
y &= \frac{c}{x_1^2} + \frac{2c}{x_1}\\
0 &= \frac{c}{x_1^2}x + \frac{2c}{x_1}\\
\frac{\cancel{c}x}{x_1^\cancel{2}} &= \frac{2\cancel{c}}{\cancel{x_1}}\\
x &= 2x_1
\end{aligned}
\end{equation}
$
It also shows that the $x$-intercept $2x_1$ is twice the $x$-coordinate of $P$. Therefore, the
midpoint of the line segment cut from the tangent line by the coordinate axes is $P$
b.) Solving for Area of triangle,
$
\begin{equation}
\begin{aligned}
\text{Area } &= \frac{1}{2}bh\\
\text{Area } &= \frac{1}{2} \quad \text{(x}\text{-intercept)} (y-\text{intercept)}\\
\text{Area } &= \frac{1}{\cancel{2}} \quad (\cancel{2}\cancel{x_1})\left(\frac{2c}{\cancel{x_1}}\right)\\
\text{Area } &= 2c
\end{aligned}
\end{equation}
$
It shows that no matter where $P$ is located on the hyperbola, the triangle formed by the tangent line and
coordinate axes always has the same area since the area is independent of point $P$.
Saturday, August 17, 2019
Single Variable Calculus, Chapter 3, 3.3, Section 3.3, Problem 98
Subscribe to:
Post Comments (Atom)
Why is the fact that the Americans are helping the Russians important?
In the late author Tom Clancy’s first novel, The Hunt for Red October, the assistance rendered to the Russians by the United States is impor...
-
There are a plethora of rules that Jonas and the other citizens must follow. Again, page numbers will vary given the edition of the book tha...
-
The only example of simile in "The Lottery"—and a particularly weak one at that—is when Mrs. Hutchinson taps Mrs. Delacroix on the...
-
A good thesis statement presents a claim (an interpretive stance on a story that can be defended using textual evidence) and is a position w...
-
The given two points of the exponential function are (2,24) and (3,144). To determine the exponential function y=ab^x plug-in the given x an...
-
What does the hot air balloon symbolize? To the Assad son who buys the hot air balloon, it symbolizes a kind of whimsy that he can afford. B...
-
The play Duchess of Malfi is named after the character and real life historical tragic figure of Duchess of Malfi who was the regent of the ...
-
Allie’s baseball mitt is extremely important to Holden in The Catcher in the Rye. It is a symbol of Allie since it was important to his brot...
No comments:
Post a Comment