3D Coordinate Geometry - Equation of a Plane
A plane is a flat, two-dimensional surface that extends infinitely far. A plane is the two-dimensional analog of a point (zero dimensions), a line (one dimension), and three-dimensional space. A plane in three-dimensional space has the equation
where at least one of the numbers  and  must be non-zero. A plane in 3D coordinate space is determined by a point and a vector that is perpendicular to the plane.
A plane in 3D coordinate space is determined by a point and a vector that is perpendicular to the plane. Let  be the point given, and  the orthogonal vector. Also, let  be any point in the plane, and  and  the position vectors of points  and  respectively. Now, if we let  then since  is perpendicular to  we have
 We can also write the above equation of the plane as
where 
This does not quite work if one of  is zero.In that case the vector is parallel to one of the coordinate planes. Say then the vector is parallel to the -plane and the equation of the required plane is  which is of course a straight line in the  plane and  is unrestricted. Similar arguments apply if two of  are zero.
Another way to think of the equation of the plane is as a flattened parallelepiped. A flattened parallelepiped, made of three vectors , has volume 0. We can use the scalar triple product to compute this volume:
where  gives the vector that is normal to the plane.
Let's say that the endpoints of  are  and  and the components of  are . Then by taking the dot product, we get the equation of a plane, which is
We can also write the above equation of the plane as
where 
This does not quite work if one of  is zero.In that case the vector is parallel to one of the coordinate planes. Say then the vector is parallel to the -plane and the equation of the required plane is  which is of course a straight line in the  plane and  is unrestricted. Similar arguments apply if two of  are zero.
Another way to think of the equation of the plane is as a flattened parallelepiped. A flattened parallelepiped, made of three vectors , has volume 0. We can use the scalar triple product to compute this volume:
where  gives the vector that is normal to the plane.
Let's say that the endpoints of  are  and  and the components of  are . Then by taking the dot product, we get the equation of a plane, which is
A plane is a flat, two-dimensional surface that extends infinitely far. A plane is the two-dimensional analog of a point (zero dimensions), a line (one dimension), and three-dimensional space. A plane in three-dimensional space has the equation
where at least one of the numbers  and  must be non-zero. A plane in 3D coordinate space is determined by a point and a vector that is perpendicular to the plane.
A plane in 3D coordinate space is determined by a point and a vector that is perpendicular to the plane. Let  be the point given, and  the orthogonal vector. Also, let  be any point in the plane, and  and  the position vectors of points  and  respectively. Now, if we let  then since  is perpendicular to  we have

We can also write the above equation of the plane as
where 
This does not quite work if one of  is zero.In that case the vector is parallel to one of the coordinate planes. Say then the vector is parallel to the -plane and the equation of the required plane is  which is of course a straight line in the  plane and  is unrestricted. Similar arguments apply if two of  are zero.
Another way to think of the equation of the plane is as a flattened parallelepiped. A flattened parallelepiped, made of three vectors , has volume 0. We can use the scalar triple product to compute this volume:
where  gives the vector that is normal to the plane.
Let's say that the endpoints of  are  and  and the components of  are . Then by taking the dot product, we get the equation of a plane, which is
The equation of a plane which is parallel to each of the -, -, and -planes and going through a point  is determined as follows:
 1) The equation of the plane which is parallel to the -plane is
1) The equation of the plane which is parallel to the -plane is  
2) The equation of the plane which is parallel to the -plane is  
3) The equation of the plane which is parallel to the -plane
The equation of a plane which is parallel to each of the -, -, and -planes and going through a point  is determined as follows:

1) The equation of the plane which is parallel to the -plane is  
2) The equation of the plane which is parallel to the -plane is
3) The equation of the plane which is parallel to the -plane
2) The equation of the plane which is parallel to the -plane is
3) The equation of the plane which is parallel to the -plane
Normal Vector and a Point
If we know the normal vector of a plane and a point passing through the plane, the equation of the plane is established.
Thus, the equation of a plane through a point  whose normal vector is  is
 
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