This document discusses parabolas as a type of conic section. It defines key properties of parabolas including the vertex, focal length, latus rectum, and directrix. The standard and vertex forms of the parabolic equation are presented. Methods for graphing parabolas by plotting points from an equation are described. An example problem calculates the depth of a satellite dish with a parabolic cross-section given its width and the distance to the focus. Real-world applications of parabolas in satellite dishes, heaters, and arched structures are briefly mentioned.

1. BY S.VARSHA
CLASS XI
SRI JAYENDRA SWAMIGAL VIDHYA
KENDRA
V.M CHATRAM

2.  Conic sections, also called conic, in geometry,
any curve produced by the intersection of a plane and a
right circular cone. .
 Conics may also be described as plane curves that are the
paths (loci) of a point moving so that the ratio of its
distance from a fixed point (the focus) to the distance
from a fixed line (the directrix) is a constant, called
the eccentricity of the curve.
 If the eccentricity is zero, the curve is a circle; if equal to
one, a parabola; if less than one, an ellipse; and if greater
than one, a hyperbola
 Every conic section corresponds to the graph of a second
degree polynomial equation of the
form Ax2 + By2 + 2Cxy + 2Dx + 2Ey + F = 0

3.  Parabola is as a conic section, created from the intersection of a
right circular conical surface and a plane parallel to another plane
that is tangential to the conical surface.
THE VERTEX
The point where the parabola intersects its axis of symmetry is
called the "vertex" and is the point where the parabola is most
sharply curved
THE FOCAL LENGTH
The distance between the vertex and the focus, measured along
the axis of symmetry, is the focal length.
THE LATUS RECTUM
The latus rectum is the chord of the parabola that is parallel to the
directrix and passes through the focus.
THE DIRECTRIX
The directrix of a parabola is a line that is perpendicular to the
axis of the parabola. The directrix of the parabola helps in defining
the parabola.

5.  The equation of parabola can be expressed in two
different ways, such as the standard form and the vertex form.
The standard form of parabola equation is expressed as follows:
 f(x) = y= ax2 + bx + c
GRAPHING THE PARABOLA
 Two points define a line. Since parabola is a curve-shaped
structure, we have to find more than two points here, to plot it.
 We need to determine at least five points as a medium to design a
leasing shape.
 In the beginning, we draw a parabola by plotting the points.
 Suppose we have a quadratic equation of the form y=ax2+ bx +
c, where x is the independent variable and y is the dependent variable.
 We have to choose some values for x and then find the
corresponding y-values. Now, these values of x and y values will
provide us with the points in the x-y plane to plot the required
parabola.
 With the help of these points, we can sketch the graph.
EXAMPLE
GRAPHS

6. PROBLEM
 An engineer designs a satellite dish with a parabolic cross section. The dish is 5 m
wide at the opening, and the focus is placed 1 2 . m from the vertex
 (a) Position a coordinate system with the origin at the vertex and the x -axis on the
parabola’s axis of symmetry and find an equation of the parabola.
 (b) Find the depth of the satellite dish at the vertex.
 SOLUTION FOR (A):
The equation for the given parabola is
y2 = 4ax

7.  SOLUTION FOR (B)
 y2 = 4ax
 here a = 1.2
 y2 = 4(1.2)x
 y2 = 4.8 x
 The parabola is passing through the point (x, 2.5)
 (2.5)2 = 4.8 x
 x = 6.25/4.8
 x = 1.3 m
 Hence the depth of the satellite dish is 1.3 m.

8. There are many applications of parabola in real life,
 Satellite dishes use parabolas to help reflect signals that are
subsequently sent to a receiver. Because of the reflecting
qualities of parabolas, signals sent directly to the satellite will
bounce off and return to the receiver after bouncing off the
focus .
 The reflecting properties of parabolas are used in several
heaters. The heat source lies in the centre, with parallel beams
concentrating the heat.
 parabolic arches have the most thrust at their bases and can
span the greatest distances when the weight is spread uniformly
over the arch.Parabolas and similar curves are often used to
make pleasing arches and shapes in buildings and bridges.