Plane Geometry – Definition With Examples

Table of Contents

    Brighterly joyfully welcomes you back to our ongoing mathematical journey. Today’s adventure delves into a corner of the mathematical universe that often goes unappreciated: Plane Geometry. This magical realm of mathematics offers countless insights and ways to understand the world around us. But what makes plane geometry so special?

    Plane Geometry is the study of flat shapes, the kind of shapes children draw when they first pick up a crayon or a piece of chalk. It’s the world of circles, triangles, and rectangles, of angles and lines. But plane geometry is not only about shapes and lines, it also includes the relationships between these figures and their properties.

    What is Plane Geometry?

    Plane Geometry is a fascinating branch of mathematics that deals with figures lying in a flat surface called a “plane.” These figures can include various shapes like circles, triangles, rectangles, and lines, among others. It is unique as it focuses entirely on these flat shapes and their properties, instead of three-dimensional shapes, which fall under the umbrella of solid geometry. In our everyday life, we often interact with these plane shapes without realizing it. For instance, when drawing a diagram or a map, we are effectively using the principles of plane geometry.

    How to Identify a Plane in Geometry?

    Identifying a plane in geometry can be tricky at first, but once you understand the concept, it gets easier. Picture this: You’re at the beach, and you draw a perfectly straight line in the sand. Now, imagine that this line extends endlessly in both directions – you’ve just imagined a plane! In more mathematical terms, a plane is a two-dimensional flat surface that extends indefinitely in every direction. It’s named with a single uppercase letter, usually located at one of its corners. Moreover, a plane can also be defined by three non-collinear points (points not lying in a single line).

    How do you Make a Plane in Math?

    Creating a plane in math might seem like an abstract concept, but it’s quite straightforward when we break it down. You start by defining two lines that don’t intersect (parallel lines). Imagine these lines extending indefinitely in both directions. The area between these lines, extended infinitely, forms a plane. Alternatively, as mentioned earlier, you can also define a plane using three non-collinear points.


    A point in plane geometry is a specific location on a plane. It’s considered to have no size — no length, width, or height. It merely marks a position. We usually represent a point with a dot and label it with a capital letter.


    A line is a straight one-dimensional figure that has no thickness and extends endlessly in both directions. It’s determined by two points, and all points on the line are in a straight path.

    Identify Plane in a Three-Dimensional Space

    Identifying a plane in three-dimensional space can be visualized like a sheet of paper floating in the air, extending indefinitely. This plane can tilt, move up and down, or side to side, but it always remains flat and extends forever.

    Basic Terminologies in Plane Geometry

    In plane geometry, there are some basic terminologies that we need to familiarize ourselves with, such as point, line, angle, and circle. A point denotes a location, a line represents a straight path, an angle measures the space between two intersecting lines, and a circle is a closed shape with all points equidistant from a central point.

    What Is a Point?

    As discussed, a point represents a specific location in plane geometry. It’s usually denoted with a dot and labelled with a capital letter.

    What Is a Line?

    A line is a one-dimensional figure extending infinitely in both directions. It’s determined by two points, and all points on the line are in a straight path.

    Angles in Plane Geometry

    An angle in plane geometry is formed when two lines intersect at a common point. The angle measures the rotation or turn between these two lines and is usually measured in degrees.

    Types of Angles

    Angles come in different types based on their measurements. These include acute angles (less than 90 degrees), right angles (exactly 90 degrees), obtuse angles (more than 90 but less than 180 degrees), and straight angles (exactly 180 degrees).

    Circle in Geometry

    A circle is a plane figure where all points are equidistant from a fixed central point. The fixed distance from the center to any point on the circle is called the radius, and the longest distance across the circle passing through the center is the diameter.

    Parallel Planes

    Parallel planes are planes that never intersect. Imagine two sheets of paper extending forever without ever touching each other. That’s what parallel planes are like!

    Intersecting Planes

    When two planes cross each other, they form a line of intersection. These are called intersecting planes. Picture two endless sheets of paper crossing each other at a line.

    Properties of a Plane

    Some of the key properties of a plane are that it is a flat, two-dimensional surface that extends indefinitely. It contains infinite lines and points. Any three non-collinear points in a plane can determine it, and if two planes aren’t identical, they are either parallel or intersecting.

    Solved Examples on Plane

    Let’s take a look at some solved examples to better understand the concepts. For instance, consider three non-collinear points A, B, and C. These three points can define a plane, which we can call Plane P.

    Practice Questions on Plane

    For practice, try answering these questions:

    1. How many points are required to define a plane?
    2. What are parallel planes? Give an example from your surroundings.
    3. Define a line and an angle.


    Wrapping up, plane geometry, with its seemingly simple figures and principles, is a key pillar of the mathematical world. It serves as the building block for understanding complex concepts in higher mathematics and physics. Its concepts extend beyond the classroom, permeating various aspects of our lives — from the architectural blueprints that shape our cities to the intricate patterns in nature, and even the GPS systems that guide us on our journeys.

    At Brighterly, we want to ignite your child’s imagination and critical thinking skills by making these abstract concepts accessible and engaging. After all, every great mathematician, scientist, or engineer started as a child who was fascinated by the world and wanted to understand it better. So, let’s continue nurturing that curiosity and thirst for knowledge. Plane geometry is not just about shapes and lines — it’s about observing, understanding, and innovating.

    Frequently Asked Questions on Plane

    What is a plane in geometry?

    In geometry, a plane is a flat, two-dimensional surface that extends indefinitely in all directions. It has no thickness and contains infinite points and lines. It’s like an endless piece of paper on which we can draw geometric figures.

    How do you define a plane in three-dimensional space?

    In three-dimensional space, a plane can be defined or visualized as a flat, infinite sheet floating in the air. This plane can move in any direction — up, down, side to side — but it always remains flat and extends forever. In mathematical terms, a plane can be defined by three non-collinear points (points not lying in a straight line) or two parallel lines.

    What is the difference between a line and a plane?

    A line is a one-dimensional figure that extends infinitely in two directions, whereas a plane is a two-dimensional surface extending infinitely in all directions. You can think of a line as lying entirely within a plane, but a plane can never be contained within a line.

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