If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Lesson 1: Types of plane figures

# Plane figures: FAQ

## What's the difference between a line and a line segment?

A line goes on forever in both directions, while a line segment has two endpoints.
Try it yourself with this exercise:

## What are the different types of angles?

There are three main types of angles: acute (less than ${90}^{\circ }$), right (${90}^{\circ }$), and obtuse (more than ${90}^{\circ }$).
Try it yourself with these exercises:

## What is the difference between parallel and perpendicular lines?

Parallel lines are two or more lines that never intersect, no matter how far they are extended. They always maintain the same distance from one another.
Perpendicular lines, on the other hand, are two lines that intersect at a right angle (90 degrees). So, while both terms refer to the relationship between two lines, they are different relationships.
Try it yourself with these exercises:

## How can I tell if a shape has line symmetry?

If you can draw a line through the shape and the two halves match up exactly, the shape has line symmetry.
Try it yourself with these exercise:

## Where do we use the concepts from this unit in the real world?

There are countless applications! For example, architects use the concepts of parallel and perpendicular lines when designing buildings, and artists use symmetry to create balanced and aesthetically pleasing works.

## Want to join the conversation?

• Is symmetry and angles part of math or geometry?
• Symmetry is part of both math and geometry because geometry is a type of math.
• hi i like math
• good for you
• im still very confused with perpendiculars actually like how do we find them? or why do we need them?
• perpendicular lines are intersecting lines but with 90 degree angles
• A Question
• What Question
• how do I know what it is? Like is it a segment? or line?
• There's three terms that look similar, but describe different figures. They're lines, rays and segments.

The key similarity is that both need to connect atleast two points. Let's call these points A and B. So what's the difference you may ask?

-Lines: Lines connect these points, but continue past them, they don't have a start or an end.

-Rays: Rays also connect A and B, but start at one of these points and they don't stop afterwards. So they have a start, but no end.

-Segments: Segments connect A and B, but don't continue past them, so they have a start and an end (A and B).

Summary:
Lines = No start no end.
Rays = Start, but no end.
Segments = Start and end.

Hope this clarifies things.
• Where did plane figures originate from?
• Hi! Plane figures originated from ancient Greeks. :)