<P> In geometric figures, angles may also be identified by the labels attached to the three points that define them . For example, the angle at vertex A enclosed by the rays AB and AC (i.e. the lines from point A to point B and point A to point C) is denoted ∠ BAC (in Unicode U + 2220 ∠ ANGLE) or B A C ^ (\ displaystyle (\ widehat (\ rm (BAC)))). Sometimes, where there is no risk of confusion, the angle may be referred to simply by its vertex ("angle A"). </P> <P> Potentially, an angle denoted, say, ∠ BAC might refer to any of four angles: the clockwise angle from B to C, the anticlockwise angle from B to C, the clockwise angle from C to B, or the anticlockwise angle from C to B, where the direction in which the angle is measured determines its sign (see Positive and negative angles). However, in many geometrical situations it is obvious from context that the positive angle less than or equal to 180 degrees is meant, and no ambiguity arises . Otherwise, a convention may be adopted so that ∠ BAC always refers to the anticlockwise (positive) angle from B to C, and ∠ CAB to the anticlockwise (positive) angle from C to B . </P> <Ul> <Li> Angles smaller than a right angle (less than 90 °) are called acute angles ("acute" meaning "sharp"). </Li> <Li> An angle equal to 1 / 4 turn (90 ° or π / 2 radians) is called a right angle . Two lines that form a right angle are said to be normal, orthogonal, or perpendicular . </Li> <Li> Angles larger than a right angle and smaller than a straight angle (between 90 ° and 180 °) are called obtuse angles ("obtuse" meaning "blunt"). </Li> <Li> An angle equal to 1 / 2 turn (180 ° or π radians) is called a straight angle . </Li> <Li> Angles larger than a straight angle but less than 1 turn (between 180 ° and 360 °) are called reflex angles . </Li> <Li> An angle equal to 1 turn (360 ° or 2π radians) is called a full angle, complete angle, or a perigon . </Li> <Li> Angles that are not right angles or a multiple of a right angle are called oblique angles . </Li> </Ul> <Li> Angles smaller than a right angle (less than 90 °) are called acute angles ("acute" meaning "sharp"). </Li>

An angle that measures greater than 0 degrees and less than 90 degrees