An angle is a measure of the amount of turning between two
E.g., the minute hand of a clock turns through one-third of
a revolution in 20 minutes; to turn from facing north to facing
west you would turn through a quarter of a revolution anti-clockwise.
The angle between two lines is the amount of turn required
to rotate one of the lines onto the other about their common
The term angle is also used whenever two lines meet at a point,
called the vertex of the angle. For example, a triangle has
three angles. The angle at vertex A is referred to as ∠BAC,
the angle at B as ∠ABC and the angle at C as
are usually measured in degrees using a protractor or angle
measurer. One complete turn is 360°, usually written
as 360°. A quarter of a turn, known as a right angle,
is equal to 90°.