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Angles are measured in degrees which is denoted by , a small circle raised above the text in the same fashion as an exponent (or a superscript).

Angles can also be measured in radians. At high school level you will only use degrees, but if you decide to take maths at university you will learn about radians.

Angle labelled as B ^ , C B A or A B C
Examples of angles. A ^ = E ^ , even though the lines making up the angles are of different lengths.

Measuring angles

The size of an angle does not depend on the length of the lines that are joined to make up the angle, but depends only on how both the lines are placed as can be seen in [link] . This means that the idea of length cannot be used to measure angles. An angle is a rotation around the vertex.

Using a protractor

A protractor is a simple tool that is used to measure angles. A picture of a protractor is shown in [link] .

Diagram of a protractor.


Using a protractor

  1. Place the bottom line of the protractor along one line of the angle so that the other line of the angle points at the degree markings.
  2. Move the protractor along the line so that the centre point on the protractor is at the vertex of the two lines that make up the angle.
  3. Follow the second line until it meets the marking on the protractor and read off the angle. Make sure you start measuring at 0 .

Measuring angles : use a protractor to measure the following angles:

Special angles

What is the smallest angle that can be drawn? The figure below shows two lines ( C A and A B ) making an angle at a common vertex A . If line C A is rotated around the common vertex A , down towards line A B , then the smallest angle that can be drawn occurs when the two lines are pointing in the same direction. This gives an angle of 0 . This is shown in [link]

If line C A is now swung upwards, any other angle can be obtained. If line C A and line A B point in opposite directions (the third case in [link] ) then this forms an angle of 180 .

If three points A , B and C lie on a straight line, then the angle between them is 180 . Conversely, if the angle between three points is 180 , then the points lie on a straight line.

An angle of 90 is called a right angle . A right angle is half the size of the angle made by a straight line (180 ). We say C A is perpendicular to A B or C A A B . An angle twice the size of a straight line is 360 . An angle measuring 360 looks identical to an angle of 0 , except for the labelling. We call this a revolution .

An angle of 90 is known as a right angle .

Angles larger than 360

All angles larger than 360 also look like we have seen them before. If you are given an angle that is larger than 360 , continue subtracting 360 from the angle, until you get an answer that is between 0 and 360 . Angles that measure more than 360 are largely for mathematical convenience.

  • Acute angle : An angle 0 and < 90 .
  • Right angle : An angle measuring 90 .
  • Obtuse angle : An angle > 90 and < 180 .
  • Straight angle : An angle measuring 180 .
  • Reflex angle : An angle > 180 and < 360 .
  • Revolution : An angle measuring 360 .

These are simply labels for angles in particular ranges, shown in [link] .

Questions & Answers

I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
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Source:  OpenStax, Siyavula textbooks: grade 10 maths [caps]. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11306/1.4
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