# Thread: Point inside the plane

1. ## Point inside the plane

Hi,
Can i use the term below the plane for a point inside the plane i.e when Ax + By+ Cz + D< 0??
The book uses the term inside the plane and the web material which i have searched. However still some people use the phrase "below the plane". Is it same as inside the plane??
Kindly guide me.
Zulfi.

2. ## Re: Point inside the plane

Hello, zak100!

Your wording is confusing . . .

Can i use the term "below the plane" for a point inside the plane,
i.e when Ax + By+ Cz + D < 0?

The book uses the term "inside the plane" and the web material which i have searched.
However still some people use the phrase "below the plane".
Is it same as "inside the plane"?

A plane is defined by an equation: . $Ax + By + Cz + D \;=\;0$

Any point $(x,y,z)$ that satisfies the equation
. . is said to be on the plane.

With an inequality, like $Ax + By + Cz + D \;<\;0$
. . we have all the points which are below the plane.

Your book should not use the term "inside".

There is a great difference between "on the circle"
. . and "inside the circle".

Besides, "inside" means "within its boundaries".
A plane has no boundaries ... it extends infinitely.

Hi,