<Ul> <Li> An angle equal to 0 ° is called a zero angle . </Li> <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> An angle equal to 0 ° is called a zero angle . </Li> <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>

An angle that measures less than 90 degrees
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