# What is Coplanar?

In geometry, coplanar refers to a set of points, lines, or objects that all lie in the same plane. A plane is a two-dimensional surface that extends infinitely in all directions. So, when we say that something is coplanar, it means that it can be represented by a flat surface.

You probably encounter coplanar objects all the time without even realizing it. For example, think about a sheet of paper. That sheet of paper is coplanar because it is two-dimensional and exists on a flat surface. Now, think about a pencil sitting on top of that sheet of paper. The pencil and the paper are coplanar because they both exist on the same flat surface. However, if you were to pick up the pencil and hold it perpendicular to the paper, it would no longer be coplanar because it would be extending out into three-dimensional space.

### Why is Coplanar Important?

Coplanarity is an important concept in geometry for a few reasons. First, many theorems and proofs in geometry rely on the fact that certain points or objects are coplanar. Second, when we're working with three-dimensional figures, it's often helpful to flatten them down into two dimensions so that we can more easily visualize what's going on. Finally, many real-world objects are actually coplanar even though they might not appear to be at first glance.

For example, let's say you're looking at a building from the street level. The building appears to have multiple floors because each floor is stacked on top of the one below it. However, if you were to take an aerial view of the building, you would see that each floor is actually coplanar with the others—they're all just flat surfaces sitting next to each other. This can be helpful to remember when you're trying to mentally visualize how a three-dimensional object looks from different angles.

In conclusion, coplanarity is a crucial concept in geometry that describes when points or objects all lie in the same plane. It's important to understand this concept because many geometric proofs rely on it and because many real-world objects are actually coplanar even though they might not appear to be at first glance.