Angles Revision

Line: passes through two points and extends to infinity in both directions, notated  

Line segment: starts at a point and ends at a point, notated 

Ray: starts at a point and extends through a second point to infinity, notated 

Acute: an angle measuring between $0^\circ$0° and $90^\circ$90°

Right: an angle measuring exactly $90^\circ$90° 

Obtuse: an angle measuring between $90^\circ$90° and $180^\circ$180°

Straight: an angle measuring exactly $180^\circ$180° 

Reflex: an angle measuring between $180^\circ$180° and $360^\circ$360°

Revolution: an angle measuring exactly $360^\circ$360°

An angle is made by two lines joining at an APEX. We label an angle by moving from a point on one line (line, segment or ray), through the APEX to a point on the the other line (line, segment or ray).  

Angles at a Point: Angles at a point sum to  $360^\circ$360°

Angles on a line: Adjacent angles on a straight line are supplementary (add up to $180^\circ$180°)

Supplementary Angles: Sum to $180^\circ$180°

Complementary Angles: Sum to $90^\circ$90°

Vertically opposite angles are equal.  

(To help remember this, it is sometimes referred to as the X rule).