welcome!. building blocks of geometry because without geometry… life is pointless

Welcome!

Building Blocks of Geometry

Because without geometry…life is pointless

Geometry started as… Began as the study of the earth

measure

There had to be some way to use language to describe the world in terms of numbers because of the need to measure the Earth.

Geometry means… the word geometry derives from

the Greek geo (earth) from the very ancient Greek Earth Goddess Gaia

and from the word metron which means to measure (the word meter is also derived from it)

Today Geometry is …

the study of one dimensional objects such as lines and segments.

the study of the properties of two dimensional shapes such as triangles, quadrilaterals and circles.

The study of the three dimensional shapes such as cylinders, pyramids and cones.

Euclid (Greek,400 BC) Euclid established the basic rules

for constructions using only a compass and straight edge.

Euclid proposed definitions and constructions about points, lines, angles, surfaces and solids.

Deductive System

Euclidian constructions are used to study properties of lines and shapes.

Euclid created a deductive system to organize geometry properties utilizing: Premises (accepted facts)…

postulates Logical Rules (rules that can be

proven)…theorems

Building Blocks of Geometry

There are three building blocks of geometry which are referred to as the undefined terms. They are the

foundation of all the geometry:

Point Line

Plane

In Geometry all definitions are based on the terms…

point, line and plane

Using these undefined terms, you are able to define all other geometry terms and figures.

First Undefined Term:

Point The most basic building block of geometry. It has no size. It has only location.

A

●

Note: you name a point with a single upper case letter.

You represent a point with a dot

Second Undefined Term:

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

AB

●●

Note: a drawing of a line has arrowheads at each end. Those arrowheads are necessary to designate that this is a “Line”.

No Arrowheads, Not a Line.

How do you name a line?

AB

Third Undefined Term:

Plane A plane has length and width but no thickness. It is like a flat surface that extends infinitely along its length and width.

Note: Represent a plane with a four-sided figure, like a tilted piece of paper drawn in perspective.

You name a plane with a script letter.

P

Definition:

Collinear Collinear means on the same line.

Points A, B and C are collinear.

AB

C

●●

●

Definition:

Coplanar Coplanar means on the same plane.

Note: Represent a plane with a four-sided figure, like a tilted piece of paper drawn in perspective.

You name a plane with a script letter.

A

BC●

●

●

We can add segments, when we add two segments, we add their lengths.

I Do Example 1A: Using the Segment Addition Postulate

G, F and H are three collinear points (points on the same line). G is between F and H, FG = 6, and FH = 11. Find GH.

5 = GH

FH = FG + GH Seg. Add. Postulate

11 = 6 + GH – 6 –6

Substitute 6 for FG and 11 for FH.Subtract 6 from both sides.

Simplify.

We Do Example 1B: Using the Segment Addition Postulate

B is between A and C , AC = 24, and BC=5. Find AB.

You Do Example 1C: Using the Segment Addition Postulate

Q is between K and W, KQ = 13, and QW = 12. Find KW.

I Do: Example 2A: Using the Segment Addition Postulate

M is between N and O.

Find NO.

10 = 2x

NM + MO = NO Seg. Add. Postulate

17 + (3x – 5) = 5x + 2

– 2 – 2

Substitute the given values

Subtract 2 from both sides.Simplify.3x + 12 = 5x + 2

3x + 10 = 5x –3x –3x

2 2 5 = x

Simplify.Subtract 3x from both sides.

Divide both sides by 2.

I Do: Example 2A Continued

M is between N and O.

Find NO.

NO = 5x + 2

Substitute 5 for x.

Simplify.= 27

= 5(5) + 2

E is between D and F. Find DF.

We Do: Example 2B

E is between D and F. Find DE, Given:

DE=3x+8 EF= 2x+2 and DF= 30

You Do: Example 2C

Home Practice:

Worksheet titled “Segment Addition Postulate” posted at hialeahhigh.org

Geometry in Nature

Geometry in Video Games

Geometry in Basketball

Geometry in Art

What did the acorn say after it grew up?

Gee, I’m a tree!!!!

Sometime yesterday…