Download Classify Triangles

Triangles
I can describe and classify triangles by their
angles.
Modified by L. Standifer
1/2010
Big Idea:
Triangles can be classified by their
angles.
Essential Question
• What are the different types of
triangles? How is each described?
Think-Pair-Share
Let’s review what you know about
angles.
• What is a right angle?
• exactly 90°, Square Corner
• What is an obtuse angle?
• 91°-179°, Bigger than a 90° right
angle
• What is an acute angle?
• Smaller than 90°, “aww” cute
Two ways to classify
triangles...
• You may describe and classify triangles
by their inside angles or by the length of
their sides.
• Today, we will classify triangles by their
angles.
How do angles help us
describe and classify triangles?
In order to describe and classify triangles
by their angles, we need to use the same
descriptions we used to identify angles.
As we learn about classifying angles, you
will notice that we must label each of the
three angles inside a triangle.
Right Triangle
A right triangle has exactly
ONE right angle.
If it has a square corner
- it’s a right triangle!
Right Triangle
Steps to classify triangles: 1.
Label all of the corners.
Acute
2. Count how many angles
are right, acute, or obtuse.
3. Classify the type by how
many types of angles a
triangle has.
This one has only one
right angle and two
acute angles, so it is a
RIGHT TRIANGLE.
RIGHT
Acute
One more helpful step...
You may use a paper
with a square corner to
check a right triangle!
Line up the corner of the right
angle triangle and the corner
of the paper to see if it is
exactly 90°.
Acute
Acute
Right
Label the angles to classify these triangles. Use a corner
of paper to check. Do all of the triangles have 1 right
angle and 2 acute angles?
Yes, this is also a right triangle!
...and more right triangles!
Obtuse
Triangle
Has one obtuse angle An obtuse triangle has exactly
ONE obtuse angle.
If it has an obtuse angle - it’s
an obtuse triangle!
obtuse
Obtuse Triangle
Remember to use the
classifying triangle steps!
acute
1. Label all of the corners.
2. Count how many angles
are right, acute, or obtuse.
3. Classify the type by how
many types of angles a
triangle has.
If it has an obtuse angle it’s an obtuse triangle!
obtuse
acute
Obtuse
triangles...
Sometimes an angle is hard
to classify. You can use the
paper trick to make sure an
angle is bigger than a 90°
angle.
Acute Triangle
acute
Has three acute angles ALL the angles are acute.
If you check all three angles
and they are smaller than 90°,
it’s acute!
(or AAA triangle)
acute
acute
Are these all acute
triangles?
Yes, all of these have
three acute angles, so they
are all acute triangles!
Take a look at these
triangles - what are they?
1.
3.
2.
6.
4.
Take out your slate and
number it - then tell me
what it is!
5.
How did you do?
1.
Acute
3.
Right
Obtuse
2.
6.
4.
5.
Obtuse
Right
Acute
Showdown Using your slates...
• Tell me what makes a right triangle?
• What makes an obtuse triangle?
• What is an acute triangle?
Answer each question - then show and share with your
group. Compare answers and discuss any