Lesson 25
Section 11.1
Parabolas
1
The graphs above represent
parabolas.
A
horizontal parabola
will open left or right.
A
vertical parabola
opens up or down.
A
parabola
is the set of all points in a plane ( only 2 dimensions) equidistant from a
fixed point
F
(the
focus
) and a fixed line
l
(the
directrix
) that lie in the plane.
The
axis
of the parabola is the line through
F
that is perpendicular to the directrix.
The
vertex
of the parabola is the point
V
on the axis halfway from
F
to
l
.
The vertex is
the point on the parabola that is closest to the directrix.
The fixed point, the focus,
will always be ‘inside’ the
parabola and the fixed line,
the directrix, will always be
‘outside’ of the parabola.
Every point on the
parabola, represented by B
in the picture, the distance
from B to the focus F is
equal to the distance from
B perpendicular to the line
at point C.
VERTEX
A horizontal parabola
has a horizontal axis.
A vertical parabola
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 Spring '08
 DELWORTH
 Algebra, Trigonometry, Cartesian Coordinate System, Euclidean geometry

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