Welcome Back!

1. Entry Task on your desks. Please start it. If you don’t have a compass, there are some over on the counter.

2. If you have your signed syllabus, please put it in the folder. 3. If you have your letter, please put it in the folder.

1.1REVIEW OF SOME BASIC IDEASUndefined Terms of Geometry

Point, line, plane, distance along a line, betweenness, space, and distance around a circular arc are all left as undefined terms: That is

they are only given intuitive descriptions. BUT FROM THESE we can define everything else in Geometry. The

entire system depends on these!

Giving the undefinable a description…• Point – Most basic building block of geometry. It has no size. It only

has a location. Named with a capital letter. A

Point A

Line – a straight, continuous arrangement of infinitely many points. It has infinite length but no thickness. It extends forever in two directions.

We call this Line l or

l

PLANE – has length and width but no thickness. It is like a flat surface that extends infinitely along its length and width. Can be named plane ABC or Plane K.

A segment is a part of a line that consists of two endpoints and all the points in between them .We name it with the two end points. Segment AB or . AB without the bar or the word means the length of the segment.

A circle is the set of all points in a plane that are equidistant from a given point. This is circle A.

Radius – a segment that goes from the Center of a circle to a point on the circle.

Both and AB are considered the radius.What’s the difference?

An equilateral triangle is a triangle with three congruent sides.

A

B C

HOW WOULD EUCLID DO IT?