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geometry Mathematical discipline that studies the relations between points, straight lines, curves, surfaces and volumes. obtuse angle Angle between 90° and 180°.

acute angle Angle that is smaller than a right angle (less than 90°).

right angle Angle formed by two lines or two perpendicular planes that measures 90°.

perpendicular Symbol denoting that a straight line meets another at a right angle.

is not parallel to Symbol denoting that two straight lines do not remain at a constant distance from one other.

is parallel to Symbol denoting that two straight lines remain at a constant distance from one another.

minute Symbol placed in superscript after a number that denotes degrees in sixtieths of a measure.

second Symbol placed in superscript after a number that denotes degrees in sixtieths of a minute.

pi Constant that represents the ratio of a circle’s circumference to its diameter; its value is approximately 3.1416.

degree Symbol placed in superscript after a number to denote the opening of an angle or the length of an arc, or in front of an uppercase letter to identify a scale of measurement.