In geometry, a **line** is an infinitely thin, infinitely long collection of points extending in two opposite directions. A closed interval corresponding to a finite portion of an infinite line is called a **line segment**. A line segment has two endpoints. A closed line segment includes both endpoints, while an open line segment excludes both endpoints; a half-open line segment includes exactly one of the endpoints.

Imagine a line – it has no beginning and no end.

Now somewhere, anywhere, put a point on it, and chop off one part – what you have now is called a ray. It has one endpoint and stretches infintely in one direction.

If you do the same on the some other part of the line you get a line segment.

## Angles

A plane is a flat endless surface. An **angle** is a part of a plane enclosed by two rays. They are measured in degrees which are denoted by .

equals – minutes, and – seconds, furthermore one minute equals 60 seconds, .

An agnle has three parts: a vertex and two rays, sometimes reffered to as arms.

Angles are divided into six groups based on their measure. Acute, right, obtuse, straight, reflex and a full rotation angles.

**Acute angles** have a measure less than .

Angles with a measure exactly are called **right angles.**

**Obtuse angles** have a measure greater than .

Angles with a measure exactly are called **straight angles**. Their arms make a straight line.

**Reflex angle** has more than and less than .

**Full rotation** always has exactly .

Angles can also be measured in radians, where equals , equals , and equals .

**Converting radians into degrees**

Full rotation has or radians. To convert radians into you have to multiply it by 180 and divide with

By dividing with two, has radians. If we multiply with and divide it with , we get .

We can generalize that with a formula:

Degrees = radians * . Let’s see how it works.

Convert into degrees.

Degrees =

### Converting degrees into radians

Opposite, when converting radians degrees into radians, for example into , you have to divide with and multiply with .

Radians = degrees * .

Convert into radians.

Radians =

## Constructing angles

**Constructing a degree angle**

Let’s say you have your side c and points A and B. And you want to construct an angle with measure of in point A.

This angle is enclosed by sides c and b, so you’ll construct your angle in point A. Draw a circle around your point A, it does not matter which radius you chose. Mark intersection of the circle with side c with D. Now draw a circle, with center in D, with the same radius you used to draw previous circle.

Draw a straight line that goes through point A and intersection of two circles you drew. You got a line which contains side b. And you got your angle.

**Constructing a degree angle**

Constructing angle whose measure equals to is very easy since we know how to construct an angle with measure . , and that means that we’ll simply construct two angles of and add them together. Put the needle in your compass in point F-intersection of your circle with previous angle and draw another arc with the same radius.

**Constructing a degree angle**

For constructing an angle with the measure of you’ll have to know how to bisect an angle. Since , we’ll firstly draw angle with . Mark the intersections of arms of an angle and circle with H and C.

We’ll put the needle of a compass in C and make an arc somewhere between H and C and do the same with H, then connect their intersection with our starting point and we got .

Other angles are constructed by combining these. If you want an angle whose measure equals to 15ᵒ you’ll simply bisect angle of 30ᵒ.

If you want 90ᵒ you’ll have to make twice 60ᵒ angle, and bisect the other one to get 30ᵒ and you’ll have 30ᵒ + 60ᵒ = 90ᵒ.

## Line segments and angles worksheets

__Line segments__

**Constructing line segments** (173.2 KiB, 317 hits)

**Constructing angles** (118.4 KiB, 352 hits)

**Construction of angle bisectors** (438.2 KiB, 327 hits)

**Measuring lines in centimeters** (105.0 KiB, 392 hits)

**Measuring lines in millimeters** (73.8 KiB, 412 hits)

__Angles__

**Determine a type of angle** (238.2 KiB, 382 hits)

**Angle relationship** (381.1 KiB, 328 hits)

**Measure an acute angles** (61.1 KiB, 354 hits)

**Measure an obtuse angles** (57.5 KiB, 363 hits)

**Angle measurement** (334.9 KiB, 314 hits)

**Draw an acute angle** (50.6 KiB, 509 hits)

**Draw an obtuse angle** (78.1 KiB, 352 hits)

**Draw different type of angles** (251.6 KiB, 257 hits)

**Converting degrees into radians** (121.2 KiB, 401 hits)

**Converting radians into degrees** (135.3 KiB, 383 hits)

**Coterminal angles** (136.9 KiB, 435 hits)