Sectieoverzicht
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An angle is formed when two lines meet or intersect at a point (called a vertex). We measure the size of the angle between the two lines in degrees. Here is some of the basic terminology used to describe and work with angles.
- Angles smaller than \({90}^\circ\) are called acute angles.
- Angles equal to \({90}^\circ\) are called right angles.
- Angles between \({90}^\circ\) and \({180}^\circ\) are called obtuse angles.
- Angles of \({180}^\circ\) are called straight angles and are on a straight line.
- Angles between \({180}^\circ\) and \({360}^\circ\) are called reflex angles.
- Angles that add up to \({90}^\circ\) are called complementary angles.
- Angles that add up to \({180}^\circ\) are called supplementary angles.
- If two straight lines intersect each other, four angles are created. The vertically opposite angles in this case are equal. In the diagram below, \(\angle\( {A}_{1} \)=\angle\( {A}_{2} \)=\angle\( {A}_{3} \)=\angle\( {A}_{4}\)\).
For a visual summary of the special lines and angles discussed, watch the next video.
Try the activity on Geometry of straight lines to make sure you understand the different types of angles formed on straight lines.-
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Leerlingen moetenAls voltooid aanduiden
Exercise: Constructions
You will need a compass, a set square and a pencil for the constructions.
Constructing a perpendicular line
Watch the next video to learn two different methods for constructing a perpendicular line.
Bisecting an angle
The next video shows you how to bisect an angle using a compass and a ruler.
Constructing a parallel line to a given line