Angles
An angle is a measure of a turn, measured in degrees or °. There are 360° in a full turn.
You can find out the size of an angle using a protractor.
You can find out the size of an angle using a protractor.
What are angles?
Angles are a measure of turn. Follow these simple rules for angles:
Angles are measured in degrees. The sign for degrees is °.
One whole turn is 360°. a is an example of a whole turn.
One quarter turn is 90° or a right angle. b is an example of a quarter turn.
One half turn is 180° or a straight line. c is an example of a half turn.
Angles are measured in degrees. The sign for degrees is °.
One whole turn is 360°. a is an example of a whole turn.
One quarter turn is 90° or a right angle. b is an example of a quarter turn.
One half turn is 180° or a straight line. c is an example of a half turn.
Types of angles
a) An angle less than 90° is acute.
b) An angle between 90° and 180° is obtuse.
c) An angle greater than 180° is reflex.
b) An angle between 90° and 180° is obtuse.
c) An angle greater than 180° is reflex.
Adding up angles
- The three angles inside a triangle always add up to 180°. This is shown by a and b in the example.
- All angles at a point always add up to 360°. This is shown by c in the example.
Using a protractor
Angles are measured using a protractor. You can guess the rough size of an angle by looking to see if it's acute or obtuse, but you'll need a protractor for a precise measurement.
Here's how to use a protractor to measure an angle:
Here's how to use a protractor to measure an angle:
- Line up the protractor so the 'cross hair' is exactly on the angle.
- Line up one of the lines with the 0 line on the protractor.
- See which numbers the angle comes between. If it is between 30 and 40, the angle must be thirty something degrees.
- Count the small degrees up from 30. In this example, the angle is 35°.
Perpendicular and Parallel lines
- Parallel lines are always the same distance apart, like a in the example.
- Perpendicular lines cross at right angles to each other, like b in the example.