Angles
An angle is an amount of tuning or rotation.
Angles are measured using a protractor, the unit of measurement is a degree (written as 1o).
A circle has 360o
An acute angle is between 0o and 90o.
Angle facts
Angles on a straight line add up to 180o.
a + b + c = 180o
Angles in a triangle add up to 180o.
a + b + c = 180o
Vertically opposite angles are equal.
a = b, c = d
a + c = b + d = 180o
Angles at a point add up to 360o.
a + b + c = 360o
Angles in a quadrilateral add up to 360o.
a + b + c + d = 360o
An exterior angle of a triangle equals the sum of the two opposite interior angles.
a + b = c
Angles in parallel lines
Alternate angles are equal.
Corresponding angles are equal.
Supplementary angles add up to 180o.
c + d = 180o.
Angles in polygons
There are two types of angles in a polygon: interior (inside) and exterior (outside).
For a regular polygon with n sides:
- The sum of the exterior angles is 360o
- An exterior angle = 360o ÷ n
- An interior angle + exterior angle = 180o
- The sum of interior angles = (n - 2) x 180o
For example:
Angles and a triangle.
Angles and parallel lines.
