Geometry Line, a half-line and line segment     Construction of angles; 60°, 30°, 90° and 45° (degrees)
Line, a half-line and line segment
Line is a straight one dimensional geometrical figure of infinite length.
Any pair of points uniquely determine a line, of which the segment between given points is the shortest path between them.
The intersection point A is a common point of two lines.
A line divides a plane into two half-planes  Two lines are called parallel lines, if they lie in the same plane and don’t intersect.
The point A which lies on a line divides the line into the two half-lines (rays).
The part of a line between two points is called a line segment. The line segment AB is the part of the line l  The line segment bisector
 The line segment bisector crosses the segment through the midpoint, forms a right angle and each of its points is equidistant from the segment's endpoints. Angle, measurement of angles
Angle is the figure formed by two half-lines or rays OA and OB (sides of an angle) sharing a common endpoint O called the vertex of the angle. An angle is signed AOB.  The unit of angles measure is a degree, 1° (deg). The angle of a full circle (complete revolution) equals 360 degrees.
One degree is divided by 60 minutes, 1° = 60', one minute by 60 seconds, 1' = 60". Complementary, supplementary, alternate and vertically opposite angles
Complementary angles are two angles that have the common vertex, one common side and whose sum is 90 degrees.
A sum of supplementary (adjacent) angles is equal to 180 degrees.
Any pair of angles formed between two intersecting lines and lying on the same side of one of them are called adjacent angles. The adjacent angles of two intersecting lines supplement each other.
Two angles having a sum of 360 degrees are called conjugate ( or explementary) angles. When two lines intersect at one point, they form four angles. The opposite angles on the figure above are called vertical angles. Vertical angles have the same measure.
Angles with correspondingly parallel sides either are equal one to another, or sum of them is 180 degrees.
Parallel lines intersected by a transversal (traverse) form the angles which are equal or supplementary. The angles contained between two given lines lying on opposite sides of the transversal are called alternate angles.
Two angles with mutually perpendicular sides are equal or supplementary. Angle bisector
An angle bisector is a straight line that divides an angle into two equal angles. Construction of angles; 60°, 30°, 90° and 45° (degrees)    Geometry and use of trigonometry contents - A 