Download Geometry Vocabulary

Geometry Vocabulary
Line
A straight path that continues forever in
both directions.
Endpoint
A point that STOPS a line from continuing
forever, it is a point at the end of a line
segment or ray.
Ray
A part of a line with one endpoint. The other
side continues forever.
Line Segment
● a segment means a piece or part of
something
● a line segment is a part of a line with 2
endpoints
You try!
What is the difference between a line, a line
segment, and a ray?
A line: has no endpoints
A ray: has 1 endpoint
A line segment: has 2 endpoints
Types of Lines
Some types of lines we will use are…
1. Intersecting Lines
2. Parallel Lines
3. Perpendicular Lines
Intersecting Lines
● “intersect” means to cross
● intersecting lines are lines that cross at
one point
Parallel Lines
Parallel lines are lines that remain the same
distance apart over their entire length. No
matter how far you extend them they will never
meet.
Perpendicular Lines
Perpendicular lines are two lines that cross
each other at an exact 90° right angle.
90°
You try!!
What kind of lines are these?
Parallel??
Intersecting??
Perpendicular??
Intersecting!
Those lines are intersecting lines because
they cross, but not at a 90° angle.
Diagonals
A diagonal of a polygon is any straight line
that connects two sides that are not next to
each other.
Angle
An angle formed by two rays or two line
segments that share an endpoint called a
vertex.
ANGLE!!!!
Angle Measure
A degree is the unit of measure for the size of
an angle.
The symbol for degrees is °, so we write 30
degrees as 30°.
Degrees can range from 1° to 360°.
We can measure angles with a
tool called a protractor….
Protractor: a tool to measure angles in degrees
There are 5 different kinds of
angles, based on their size...
1.
2.
3.
4.
5.
Right Angle
Acute Angle
Obtuse Angle
Straight Angle
Reflex Angle (we won’t learn about these in 4th grade)
Right Angle
A right angle is an angle that measures
exactly 90°.
90°
Acute Angle
An angle with a measure less than 90°.
You try!
Which angle is acute?
100° ?
60° ?
175°?
60° is acute because it measures
less than 90°!!
Obtuse Angle
An obtuse angle is an angle that measures
greater than 90° and less than 180°.
Straight Angle
A straight angle is an angle that measures
exactly 180°. This angle looks like a straight
line.
180°
You try it!
Which picture shows an obtuse angle?
Good job!
This angle is obtuse because its measure is
greater than 90 degrees!
Open Figures
An open figure is a figure that begins and
ends at different points.
examples:
POLYGONS
Lines can form all kinds of different shapes.
A polygon is defined as a closed figure with
three or more straight sides.
Keep in mind...
Open and closed figures may have curved
lines,
BUT
Polygons are closed figures with straight
sides only!
Classifying Polygons
Polygons are classified by the number of
sides they have.
These are the names of different polygons.
You try it!
What kind of polygon is this?
Pentagon!
This shape is a pentagon because it has five
sides.
1
2
3
5
4
TRIANGLES
Now that we know polygons and angles,
we can see how 3 sides and angles come
together and form different triangles.
Triangle
A tricycle has three wheels.
So a triangle is a polygon made up of three
sides and three angles!
Important Information
When you add all the degree measures in a
triangle, the sum of the three angles is always
equal to 180°.
Triangles are classified in two ways:
1. by the measure of their angles, and
2. by the length of their sides,
SO all triangles have TWO names!
Using Angle Measure to Classify Triangles
All triangles have at least two acute angles. You
look at the 3rd angle to classify it.
1. Acute Triangle: has 3 acute (less than 90°)
angles.
2. Right Triangle: has one right (90°) angle.
3. Obtuse Triangle: has one obtuse (greater than
90°) angle.
Right Triangle
A right triangle is a triangle with ONE right
angle.
90°
Acute Triangle
An acute triangle is a triangle with three
acute angles (angles less than 90°).
Obtuse Triangle
An obtuse triangle is a triangle with one
angle that measures greater than 90°.
greater
than 90°
You try!!
What is the difference between the angles of
acute, right, and obtuse triangles?
● acute has THREE acute angles.
● a right triangle has ONE right angle
and TWO acute angles.
● an obtuse triangle has ONE angle
greater than 90° and TWO acute
angles.
Using Length of Sides to Classify Triangles
1. Equilateral Triangle
2. Isosceles Triangle
3. Scalene Triangle
Equilateral Triangle
An equilateral triangle is a triangle with
three equal sides. (It will always have three
60° angles.)
Isosceles Triangle
An isosceles triangle is a triangle where at
least TWO side lengths are the same.
… and,
This is a scalene triangle because it has three
unequal side lengths.
Scalene Triangle
A scalene triangle describes a triangle whose
side lengths are all different so no two sides
are the same length.
Your turn !
Which picture shows a scalene triangle?
Which picture shows an isosceles triangle?
You got it !
This is an isosceles triangle because it has
TWO side lengths which are the same.
Quadrilaterals
A special type of polygon is a quadrilateral.
A quadrilateral is a polygon that has exactly
four sides. There are many types.
Quadrilaterals
A parallelogram is a quadrilateral that has
two pairs of opposite, parallel sides.
Quadrilaterals
A rhombus is a special type of parallelogram.
It has two pairs of parallel sides and all four
sides are equal.
Note: A rhombus is a
parallelogram, but not all
parallelograms are a
rhombus.
Quadrilaterals
A rectangle is a quadrilateral and
parallelogram that has four right angles.
Quadrilaterals
A square is a quadrilateral, parallelogram,
rhombus, and rectangle that has four right
angles and four equal sides.
Note: a square can be a
rectangle also because it
has four right angles.
However, a rectangle is not
a square.
Quadrilaterals
A trapezoid is a quadrilateral that has
exactly ONE pair of parallel sides.
Quadrilaterals review
What type of quadrilateral are these?
a.
b.
c.
Quadrilaterals review
a. This is a trapezoid because it has one pair of
parallel sides.
b. This is a rhombus because it has 2 pairs of
parallel sides, and all four sides are equal,
but it does NOT have 4 right angles.
c. This is a rectangle because it has four right
angles and two pair of parallel sides.
A Line of Symmetry
is used to determine if 2 parts of a figure are
congruent (exactly the same size and shape).
Lines of Symmetry
A shape has symmetry when it can be folded
in half and the two sides match up perfectly.
A shape can have more than one line of
symmetry.
Symmetry
Polygons can often have more than one line
of symmetry.
You try it!
Which of these letters has/have line
symmetry?
A
T
L
Right!
The letters A and T both have line symmetry.
A
T
Great job reviewing the
Geometry Vocabulary.
Keep practicing !