6.7: Hyperbolas and Asymptotes
Like other conic sections, hyperbolas can be created by "slicing" a cone and looking at the crosssection. Unlike other conics, hyperbolas actually require 2 cones stacked on top of each other, point to point. The shape is the result of effectively creating a parabola out of both cones at the same time.
So the question is, should hyperbolas really be considered a shape all their own? Or are they just two parabolas graphed at the same time? Could "different" shapes be made from any of the other conic sections if two cones were used at the same time?
Watch This
Embedded Video:
 Khan Academy: Conic Sections Hyperbolas 2
Guidance
In addition to their focal property, hyperbolas also have another interesting geometric property. Unlike a parabola, a hyperbola becomes infinitesimally close to a certain line as the \begin{align*}x\end{align*}
These lines are called asymptotes.
There are two asymptotes, and they cross at the point at which the hyperbola is centered:
For a hyperbola of the form \begin{align*}\frac{x^2}{a^2}  \frac{y^2}{b^2} = 1\end{align*}

\begin{align*}y = \frac{b}{a} x\end{align*}
y=bax and \begin{align*}y =  \frac{b}{a} x\end{align*}y=−bax .
For a hyperbola of the form \begin{align*}\frac{y^2}{a^2}  \frac{x^2}{b^2} = 1\end{align*}

\begin{align*}y = \frac{a}{b} x\end{align*}
y=abx and \begin{align*}y =  \frac{a}{b} x\end{align*}y=−abx .
(For a shifted hyperbola, the asymptotes shift accordingly.)
Example A
Graph the following hyperbola, drawing its foci and asymptotes and using them to create a better drawing: \begin{align*}9x^2  36x  4y^2  16y  16 = 0\end{align*}
Solution
First, we put the hyperbola into the standard form:
\begin{align*}9(x^2  4x)  4(y^2 + 4y) & = 16 \\
9(x^2  4x + 4)  4(y^2 + 4y + 4) & = 36 \\
\frac{(x  2)^2}{4}  \frac{(y + 2)^2}{9} & = 1\end{align*}
So \begin{align*}a = 2\end{align*}
Example B
Graph the following hyperbola, drawing its foci and asymptotes and using them to create a better drawing: \begin{align*}16x^2  96x  9y^2  36y  84 = 0\end{align*}
Solution
Example C
Graph the following hyperbola, drawing its foci and asymptotes and using them to create a better drawing: \begin{align*}y^2  14y 25x^2  200x 376 = 0\end{align*}
Solution
Concept question wrapup Hyperbolas are considered different shapes, because there are specific behaviors that are unique to hyperbolas. Also, though hyperbolas are the result of dual parabolas, none of the other conics really create unique shapes with dual cones  just double figures  and in any case require multiple "slices". 

Vocabulary
A hyperbola is a conic section where the cutting plane intersects both sides of the cone, resulting in two infinite “U”shapes curves.
An unbounded shape is so large that no circle, no matter how large, can enclose the shape.
An asymptote is a line which a curve approaches as the curve and the line approach infinity, eventually becoming closer than any given positive number.
A perpendicular hyperbola is a hyperbola where the asymptotes are perpendicular.
Guided Practice
Questions
1) Find the equation for a hyperbola with asymptotes of slopes \begin{align*}\frac{5}{12}\end{align*}
2) A hyperbola with perpendicular asymptotes is called perpendicular. What does the equation of a perpendicular hyperbola look like?
3) Find an equation of the hyperbola with xintercepts at x = –7 and x = 5, and foci at (–6, 0) and (4, 0).
Solutions
1) \begin{align*}\frac{(y  6)^2}{25}  \frac{(x  2)^2}{144} = 1\end{align*}
2) The slopes of perpendicular lines are negative reciprocals of each other. This means that \begin{align*}\frac{a}{b} = \frac{b}{a}\end{align*}
3) To find the equation:
 The foci have the same ycoordinates, so this is a left/right hyperbola with the center, foci, and vertices on a line paralleling the xaxis.

Since it is a left/right hyperbola, the y part of the equation will be negative and equation will lead with the \begin{align*}x^2\end{align*}
x2 term (since the leading term is positive by convention and the squared term must have different signs if this is a hyperbola). :The center is midway between the foci, so the center \begin{align*}(h, k) = (1, 0)\end{align*}(h,k)=(−1,0) . The foci c are 5 units to either side of the center, so \begin{align*}c = 5 \to c^2 = 25\end{align*}c=5→c2=25 
The xintercepts are 4 units to either side of the center, and the foci are on the xaxis so the intercepts must be the vertices a \begin{align*}a = 4 \to a^2 = 16\end{align*}
a=4→a2=16 
Use Pythagoras \begin{align*}a^2 + b^2 = c^2\end{align*}
a2+b2=c2 to get \begin{align*}b^2 = 25  16 = 9\end{align*}b2=25−16=9
Substitute the calculated values into the standard form \begin{align*}\frac{(x  h)^2}{a}  \frac{(y  k)^2}{b} = 1\end{align*}

\begin{align*}\frac{(x + 1)^2}{16}  \frac{y^2}{9} = 1\end{align*}
(x+1)216−y29=1
Practice
Find the equations of the asymptotes

\begin{align*}\frac{(y + 3)^2}{4}  (x  2)^2 = 1\end{align*}
(y+3)24−(x−2)2=1 
\begin{align*}\frac{y^2}{16}  (x + 3)^2 = 1\end{align*}
y216−(x+3)2=1 
\begin{align*}\frac{(x + 2)^2}{4}  \frac{(y + 1)^2}{9} = 1\end{align*}
(x+2)24−(y+1)29=1 
\begin{align*}\frac{(y  4)^2}{16}  \frac{(x  4)^2}{16} = 1\end{align*}
(y−4)216−(x−4)216=1 
\begin{align*}\frac{(x  1)^2}{1}  \frac{9(y + 4)^2}{1} = 9\end{align*}
(x−1)21−9(y+4)21=9 
\begin{align*}\frac{(y + 2)^2}{16}  \frac{(x  2)^2}{1} = 1\end{align*}
(y+2)216−(x−2)21=1 
\begin{align*}\frac{(x  4)^2}{1}  \frac{(y + 1)^2}{4} = 1\end{align*}
(x−4)21−(y+1)24=1  \begin{align*}\frac{y^2}{16}  \frac{(x + 1)^2}{4} = 1\end{align*}
 \begin{align*}\frac{(x  3)^2}{4}  \frac{(y  4)^2}{1} = 1\end{align*}
 \begin{align*}\frac{(x  4)^2}{4}  \frac{(y  3)^2}{1} = 1\end{align*}
Graph the hyperbolas, give the equation of the asymptotes, use the asymptotes to enhance the accuracy of your graph.
 \begin{align*}\frac{(x + 4)^2}{4}  \frac{(y  1)^2}{9} = 1\end{align*}
 \begin{align*}\frac{(y + 3)^2}{4}  \frac{(x  4)^2}{9} = 1\end{align*}
 \begin{align*}\frac{(y + 4)^2}{16}  \frac{(x  1)^2}{4} = 1\end{align*}
 \begin{align*}(x  2)^2  4y^2 = 16\end{align*}
 \begin{align*}\frac{y^2}{4}  \frac{(x  1)^2}{4} = 1\end{align*}
 \begin{align*}\frac{(x  2)^2}{16}  \frac{(y + 4)^2}{1} = 1\end{align*}
 \begin{align*}\frac{(x + 2)^2}{9}  \frac{(y + 2)^2}{16} = 1\end{align*}
 \begin{align*}\frac{(x + 4)^2}{9}  \frac{(y  2)^2}{4} = 1\end{align*}
Asymptotes
An asymptote is a line on the graph of a function representing a value toward which the function may approach, but does not reach (with certain exceptions).Conic
Conic sections are those curves that can be created by the intersection of a double cone and a plane. They include circles, ellipses, parabolas, and hyperbolas.hyperbola
A hyperbola is a conic section formed when the cutting plane intersects both sides of the cone, resulting in two infinite “U”shaped curves.Parabola
A parabola is the set of points that are equidistant from a fixed point on the interior of the curve, called the '''focus''', and a line on the exterior, called the '''directrix'''. The directrix is vertical or horizontal, depending on the orientation of the parabola.perpendicular hyperbola
A perpendicular hyperbola has asymptotes that intersect at a angle.unbounded
To be unbounded means to be so large that no circle, no matter how large, can enclose the shape.Image Attributions
Here you will learn how to identify the asymptotes of a hyperbola.
Concept Nodes:
Asymptotes
An asymptote is a line on the graph of a function representing a value toward which the function may approach, but does not reach (with certain exceptions).Conic
Conic sections are those curves that can be created by the intersection of a double cone and a plane. They include circles, ellipses, parabolas, and hyperbolas.hyperbola
A hyperbola is a conic section formed when the cutting plane intersects both sides of the cone, resulting in two infinite “U”shaped curves.Parabola
A parabola is the set of points that are equidistant from a fixed point on the interior of the curve, called the '''focus''', and a line on the exterior, called the '''directrix'''. The directrix is vertical or horizontal, depending on the orientation of the parabola.perpendicular hyperbola
A perpendicular hyperbola has asymptotes that intersect at a angle.unbounded
To be unbounded means to be so large that no circle, no matter how large, can enclose the shape.