Angles Revision
We have seen a number of definitions and introduced quite a bit of new language in Geometry so far. Let us revise what we know and practise this a little before moving on to some new work.
Line Definitions
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 
Angle Definitions
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).
Worked Example
Question 1
In the following, state the vertex and name the angle.
Question 2
Is the angle acute, obtuse or reflex?