Set the two expressions for
equal to each other and solve for
to derive the equation of the parabola. We do this because the distance from
to
equals the distance from
to
We then square both sides of the equation, expand the squared terms, and simplify by combining like terms.
The equations of parabolas with vertex
are
when the
x -axis is the axis of symmetry and
when the
y -axis is the axis of symmetry. These standard forms are given below, along with their general graphs and key features.
Standard forms of parabolas with vertex (0, 0)
[link] and
[link] summarize the standard features of parabolas with a vertex at the origin.
Axis of Symmetry
Equation
Focus
Directrix
Endpoints of Latus Rectum
x -axis
y -axis
The key features of a parabola are its vertex, axis of symmetry, focus, directrix, and latus rectum. See
[link] . When given a standard equation for a parabola centered at the origin, we can easily identify the key features to graph the parabola.
A line is said to be tangent to a curve if it intersects the curve at exactly one point. If we sketch lines tangent to the parabola at the endpoints of the latus rectum, these lines intersect on the axis of symmetry, as shown in
[link] .
Given a standard form equation for a parabola centered at (0, 0), sketch the graph.
Determine which of the standard forms applies to the given equation:
or
Use the standard form identified in Step 1 to determine the axis of symmetry, focus, equation of the directrix, and endpoints of the latus rectum.
If the equation is in the form
then
the axis of symmetry is the
x -axis,
set
equal to the coefficient of
x in the given equation to solve for
If
the parabola opens right. If
the parabola opens left.
use
to find the coordinates of the focus,
use
to find the equation of the directrix,
use
to find the endpoints of the latus rectum,
Alternately, substitute
into the original equation.
If the equation is in the form
then
the axis of symmetry is the
y -axis,
set
equal to the coefficient of
y in the given equation to solve for
If
the parabola opens up. If
the parabola opens down.
use
to find the coordinates of the focus,
use
to find equation of the directrix,
use
to find the endpoints of the latus rectum,
Plot the focus, directrix, and latus rectum, and draw a smooth curve to form the parabola.
Graphing a parabola with vertex (0, 0) and the
x -axis as the axis of symmetry
Graph
Identify and label the
focus ,
directrix , and endpoints of the
latus rectum .
The standard form that applies to the given equation is
Thus, the axis of symmetry is the
x -axis. It follows that:
so
Since
the parabola opens right
the coordinates of the focus are
the equation of the directrix is
the endpoints of the latus rectum have the same
x -coordinate at the focus. To find the endpoints, substitute
into the original equation:
Next we plot the focus, directrix, and latus rectum, and draw a smooth curve to form the
parabola .
[link]
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asegid
to transport fluids fats proteins and lymphocytes to the blood stream as lymph
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Kamara
yes
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how does the stomach protect itself from the damaging effects of HCl
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