# Intersection of planes

## Basics of Intersection of Planes

• A plane in three dimensions is defined by a point and a normal vector.
• The intersection of planes can result in a point, a line, or a plane, depending on the orientation of the planes.
• When three planes intersect at a single point, they are called concurrent planes. If three planes intersect along a line, they are referred to as coplanar planes.
• Two planes that do not intersect are parallel, and their normal vectors are either identical or proportional.

## Equations of Planes and Their Intersections

• The equation of a plane in three dimensions can be expressed in the general form `ax+by+cz=d`, where `a, b, c` represent the normal vector and `d` is a constant.
• The intersection of two planes can be found by solving the simultaneous equations that represent the two planes.

## Line of Intersection Between Two Planes

• The line of intersection between two planes can be found using the normal vectors of the two planes and a point on the line.
• The normal vectors of the two planes are perpendicular to the line, hence their cross product gives a director vector of the line.
• A point on the line of intersection can be found by setting one of the variables to zero and solving the simultaneous equations for the remaining variables.

## Relative Positions of Three Planes

• Three planes can be parallel, intersect along a line, intersect at a point, or have no common point of intersection.
• The relative positions of three planes can be determined from the solutions of their simultaneous equations, which can be solved manually, or with the use of matrices, Gaussian elimination, or Cramer’s rule.

## Applications of Intersection of Planes

• The concept of intersection of planes is extensively used in geometry to solve problems involving three-dimensional figures.
• In computer graphics, intersection of planes is used in calculations involving shading, intersections, and reflections.
• Civil engineering also uses the concept to plan and design structures.