Home » Maths » Parabola: Types of Parabolas Equations

Parabola: Types of Parabolas Equations


What is Parabola?

A parabola is a set of all points in a plane that are equidistant  from a fixed line and fixed point in the plane.

  • A line through the focus and perpendicular to the diretrix is called the axis of the parabola.
  • The point of intersection of the parabola with its axis is called the vertex of the parabola.
  • In the adjoining figure, C is a parabola with focus F and the line DD, as its directrix.

What is Parabola

If we take an arbitrary point P on the parabola and draw PM DD then by the definition of a parabola, we have PF=PM.

Different Types of Parabolas Equations

1. First Standard Equation : y =4ax, a > 0

Let X’ OX and YOY’ be the coordinate axes and let a > 0 be given.

Let us consider a parabola whose focus is F(a,0) and the directrix is the line DD’, whose equation is x+a =0.

Consider a parabola whose focus is F(a,0) and the directrix is the line DD’, whose equation is x+a =0.

Let P (x,y) be an arbitrary point on the parabola. Let PM DD’.

Standard Equation of parabola

Then, by the definition of a parabola, we have PF=PM.

 

Now, PF=PM ⇒ PF2 = PM2

⇒ (x-a)+y2 =(x+a)2

⇒ y2 = (x + a )2  – (x+a)2

⇒ y2 = (x + a )2  – (x- a)2

⇒ y =4ax (a > 0).

 

 

 

2. 2nd Standard Equation : y =-4ax, a > 0

y =-4ax (a > 0) is a parabola where,

2nd Standard Equation

  • focus is F(-a, 0)
  • vertex is O(0,0)
  • directix is the line x-a = 0
  • axis is the line y= 0
  • length of the latus rectum is 4a
  • latus rectum is the line x = -a

 

 

 

 

 

 

 

3. Upward Parabola Equation OR 3rd Standard Equation : x =4ay, a > 0

Upward Parabola Equation

x =4ay (a > 0) is a parabola where,

  • focus is F(0, a)
  • vertex is O(0,0)
  • directix is the line y+a = 0,
  • axis is the line x= 0
  • length of the latus rectum is 4a
  • latus rectum is the line y – a = 0

 

 

 

 

 

4.Downward Parabola Equation or 4th Standard Equation : x = -4ay, a > 0

Downward Parabola Equation

x =-4ay (a > 0) is a parabola where,

  • focus is F(0, -a)
  • vertex is O(0,0)
  • directix is the line y-a = 0,
  • axis is the line x= 0
  • length of the latus rectum is 4a
  • latus rectum is the line y + a = 0
error: