8.G.5
Topic & Standards of this learning cycle:
- To discover that the sum of the interior angles of any triangle equals 180
degrees.
Ideas, representations, and strategies in the learning cycle are:
- Use a modeling activity that leads into an angle measuring activity to solidify
the understanding of the standard.
The practice standards represented in this cycle are:
- A worksheet containing level 1, 2 and 3 types of questions.
The tasks we will use are:
- Angle-ectomy Activity (adapted from Glencoe Geometry 1998, p.188)
- Measuring angles of a triangle activity
- Practice worksheet
Materials needed:
- Straight edge for each student
- Protractor for each student
-
Develop:
-Angle-ectomy activity
Solidify:
-
Using a protractor and a straight edge, create 3 different triangles and
measure the angles of each
Practice:
- Worksheet on solving for the missing angles in various triangles.
-
“I can demonstrate that the sum of the angles of a triangle equals 180
degrees.”
Angle-ectomy Activity
(adapted from Glencoe Geometry textbook-1998)
1. Use a straightedge to draw a triangle.
2. Cut out your triangle and label the angles 1, 2 & 3.
3. Tear off each angle and arrange them to form 3 adjacent angles.
4. What seems to be true about the sum of the measures of the angles of a
triangle?
__________________________________________________________________
Measure the size of the following angles:
= _________________˚
= _________________˚
= _________________˚
= _________________˚
Referring to the angle-ectomy activity, what is the sum of the measures of the
angles of any triangle?
__________________________________________________________________
Sum of
the angles
Measure
of angle 3
Measure
of angle 2
Measure
of angle 1
Draw Picture
Acute Triangle
Obtuse Triangle
Right Triangle
Find the value of all unknown angles in the following:
58˚
x˚
47˚
x˚
21˚
98˚
x˚
34˚
21˚
x˚
x˚
80˚
x˚
51˚
(2x+3)˚
3x˚
(x+5)˚
x˚
90˚
2x˚
(2x-2)˚
In a right triangle, list 5 possible measures of the other two angles:
State the relationship between the measures of the angles in a triangle and how you know it is true: