Geometry:

Did you that geometry comes from the Greek words geo and metria – which means to measure (metria) land (geo), something the Greeks were very good at.

In mathematics, geometry involves the properties, measurement, and relationships of points, lines, angles, surfaces, and solids.

R

DEFINITIONS

RAYS AND LINES

A Point – is a location in space.

Line Segment – made up of 2 points and the straight path between them.

The line segment below is line segment AB:

A B

Rays – a straight path that has a starting point and goes on forever in one direction

Below is ray RA. The point R is the starting point of this ray. The point A is any point along the ray.

A line - is a straight path that goes on forever in both directions.

Below is line EF or FE

E

F

You can also write the name of this line as:

ANGLES

An angle is formed by two line segments or 2 rays that share the same endpoint (called the vertex).

T is the vertex.

An angle formed by rays – named angle T or named angle CTA or angle ATC.

We use the following symbol for the word angle:

Here are 5 classifications of angles:

Right angle 90 °

Acute angle 0 – 90 °

Obtuse angle 90° – 180 °

Straight angle 180 °

Reflex angle 180° – 360 °

PARALLEL LINES AND SEGMENTS

Parallel lines are lines on a flat surface that never meet and are always the same distance apart.

Parallel line segments are always the same distance apart.

Intersecting lines or segments cross each other.

Perpendicular lines or segments intersect at a right angle.

A B F E Parallel Segments

Intersecting Segments

A E F B Perpendicular Segments

POLYGONS

Yes, it’s another Greek word. ‘Poly’ meaning multiple or more than 2 in this case, and ‘gon’ meaning angle. So a polygon is a geometric 2-dimensional figure made up of 3 or more line segments, called sides, and has 3 or more angles.

There are 2 more requirements for a polygon:

· The sides of a polygon are connected end to end and make a closed path.

· The sides of a polygon do not cross (intersect).