Geometry Study Power Point

Welcome Elementary School 2014

Lines and Angles

4GA.1 Draw points, lines, line segments, rays, angles (right, acute, obtuse), and perpendicular and parallel lines. Identify these in two-dimensional figures.

Points and Line Segments

A B

points

When you connect two

points using a straightedge, you

create a

line segment

Points, Endpoints and Line Segments

A B

line segment• letters are often used to name a line segment

• ONE name for this line segment is “line segment AB”

• A short way to write “line segment AB” is AB

• Another name for this line segment is “line segment BA”

endpoint

endpoint

Lines

A B

lines• extending line segment AB in both directions and drawing an arrow at each end makes a LINE

• This line is called “line AB” or “line BA”

• A short way to write the name of this lines is

AB or BA

point point

Ray

C D

rays• line segment that goes on without end in only ONE

direction

• Point C is the ENDPOINT of the ray CD

• The letter that names the ENDPOINT is ALWAYS

written first.

Short way to write the name is CD

endpoint

point

What is an angle?

D O

A angle is two rays or line

segments that share a common endpoint, called

the vertex.

G

Naming AnglesA B

How to name angles:• The vertex is one way to name an angle. The angle here could be named angle B because B is the vertex of the angle.

• Remember that the middle letter in the name of the angle is always the vertex.

You should name this angle CBA or ABC.

vertex

C

Important ideas to remember about angles

• Angles can be formed by two rays or two line segments that share a common endpoint.

• The common endpoint is called the vertex.• The vertex is always named in the middle

of an angle.• When you draw an angle, make sure you

use a half circle to show the viewer where to look This shouts, look here!

2d Shapes

4GA.2 Classify two-dimensional figures based on the presence or absence of parallel or perpendicular lines, or the presence or absence of angles of a specified size. Recognize right triangles as a category, and identify right triangles.

Quadrilaterals

What is a four-sided shape called?quadrangle or quadrilateral

Literally means “4” angles or “4” sides

QUAD always means four

Triangles

A triangle is a three-sided shape.

Right Triangle - one of its angles is a right

angle (90º)Obtuse Triangle - one of its angles is bigger

than 90ºAcute Triangle - all of its angles are smaller

than 90º

Scalene - each side is a different length

Isosceles - two sides are the same length

Equilateral - all sides are the same length

Symmetry

4GA.3 Recognize a line of symmetry for a two-dimensional figure as a line across the figure such that the figure can be folded along the line into matching parts. Identify line-symmetric figures and draw lines of symmetry.

Symmetry: A figure has a line of symmetry when it can be folded along a line so that its two halves

match each other exactly.

These letters have a line of symmetry drawn.

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