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# What is Parabola,Definition,Graph

What is Parabola: If the intersecting plane is parallel to the generator of the cone but cut only one nappe is called parabola. We have already stated that a conic section is a parabola if e = 1. Here e is the eccentricity.

We shall first derive an equation of a parabola in standard form and study its important properties.

If we take the focus of the parabola as F (a, 0),\;a > 0 and its directrix as line L whose equation is x = -a, then its equation becomes very simple. Let P(x, y) be a point on the parabola.

So, by definition

\frac{\left|PF\right|}{\left|PM\right|}=1 \;\;\;\;or\;\;\;\; \left|PF\right|=\left|PM\right|

Now,

\left|PM\right|=x+a\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\; (1)

\left|PF\right|=\sqrt{(x-a)^2+(y-0)^2}

Substituting into (1), we get

\sqrt{(x-a)^2+(y-0)^2}=x+a

(x-a)^2+(y)^2=(x+a)^2

y^2=(x+a)^2-(x-a)^2

y^2=4ax

which is standard equation of Parabola

### Some Definitions:

what is parabola

• The line through the focus and perpendicular to the directrix is called axis of parabola. In case of (2), the axis is y = 0.
• The point where the axis meets the parabola is called vertex of parabola. Clearly the equation (2) has vertex .A(0,0).. The line through A and perpendicular to the axis of the parabola has equation x = 0.. It meets the parabola at coincident points and so it is a tangent to the curve at A.
• A line joining two distinct points on a parabola is called a chord of parabola. A chord passing through the focus of a parabola is called a focal chord of parabola. The focal chord perpendicular to the axis of the parabola (1) is called latusrectum of parabola. It has an equation x = a and it intersects the curve at the points where

y^2 = 4a^2 \;\;\;\;\;or\;\;\;\;\; y+\pm 2a

Thus coordinates of the end points L and L’ of the latusrectum are

L(a ,2a )\;\;\;\;\;\; and\;\;\;\;\; L'(a ,- 2a ).

The length of the latusrectum is \left|LL'\right|=4a

• The point (at^2 , 2at) lies on the parabola [/katex]y^2=4ax[/katex] for any real t.

x = at^2 \;\;\;\;\;\;\;\;\;,y = 2at

are called parametric equations of parabola y^2 = 4ax ## Author: Azhar Ali

I am graduated in Mathematics from university of Sargodha, having master degree in Mathematics. Mathematics blogger

## 5 thoughts on “What is Parabola,Definition,Graph”

1. Shahroz Javed says:

Well done , Sir . ALLAH PAK bless you and give you success in every walk of life . ALLAH PAK bless you with your best wishes and give you more and more success . May ALLAH bless you with more knowledge . InShaAlllah you(Ap) will become a big gun one day . It’s a good effort . ALLAH Ap ko kamyabiyaan ata farmaiy aur lambi umar bhi , so that you may become a pride of our country . Ameen.

1. Azhar Ali says:

thanks shahroz

2. ? says:

Love u.. 😘

1. Azhar Ali says:

love you more jnb