Angle

An angle is a measure of the amount of rotation about the point of intersection of two lines or line segments that is required to bring one into correspondence with the other.

Angle is an elementary-school-level concept. It is listed in the California State Standards for Grade 3.

Examples

Acute Angle:	An acute angle is an angle that measures less than 90 degrees.
Obtuse Angle:	An obtuse angle is an angle that measures greater than 90 degrees and less than 180 degrees.
Right Angle:	A right angle is an angle that measures exactly 90 degrees.

Prerequisites

Line:

A line is the infinite extension in both directions of a line segment, giving the path of shortest distance between two points in Euclidean space.

Classroom Articles on Plane Geometry

	Altitude	Midpoint
	Area	Parallel
	Circle	Perimeter
	Circumference	Perpendicular
	Collinear	Pi
	Complementary Angles	Plane Geometry
	Diameter	Point
	Geometric Construction	Radius
	Golden Ratio	Supplementary Angles
	Golden Rectangle	Triangle Inequality
	Hypotenuse

Classroom Articles on Geometry (Up to Elementary-School Level)

	Cone	Pentagon
	Cube	Polygon
	Cylinder	Prism
	Decagon	Pyramid
	Dodecagon	Quadrilateral
	Equilateral Triangle	Rectangle
	Hendecagon	Regular Polygon
	Heptagon	Right Triangle
	Hexagon	Sphere
	Isosceles Triangle	Square
	Nonagon	Surface Area
	Octagon	Triangle
	Parallelogram	Volume