1. Lesson Plan for SD 3.1 (50 minutes):
Target: I can identify what side lengths make a triangle.
5 minutes Warm-up (notebook)
15 minutes Try to build triangles will given side lengths (can use polystrips,
virtual polystrips on computer/iPad).
15 minutes Discuss the pattern for when side lengths do/not make a triangle.
10 minutes Summary statement (think, ink, pair, share – discuss as class)
5 minutes Reminders:
Correct homework with key (puzzle)

2. Investigation 2 : The Angle Connection
SD 3.1 Building Triangles
Learning Target: I can identify what side lengths make a triangle.
Homework: Day 2 SD 3.1 Complete p. 7 and CORRECT with the KEY
Warm-up:
Find the missing angles in the triangle: B A C

3. x + 2x + 24 = 180
3x + 24 = 180
3x = 156
x = 52
∠BAD = x = 52⁰
∠ACB = 2x = 104⁰
∠CBA = 24⁰
Check: = 180⁰

4. Inv. 3 - Problem 3.1: Building Triangles
Virtual Polystrips
Side Lengths
3, 4, 5
1, 1, 3
2, 4, 7
Triangle Possible?
Sketch Triangle
2, 3, 4
4, 5, 7
2, 3, 8
Answers on next pages

5. Virtual Polystrips http://media. pearsoncmg
3, 4, 5
1, 1, 3
Yes! No
2, 3, 4
2, 4, 7
Yes! No

6. 4, 5, 7
Yes!
2, 3, 8 No

7. Yes! No No Yes! Yes! No Inv. 3 - Problem 3.1: Building Triangles
Virtual Polystrips
Side Lengths
3, 4, 5
1, 1, 3
2, 4, 7
Triangle Possible?
Sketch Triangle
2, 3, 4
2, 3, 8
Yes! No No
Yes!
Yes! No
Answers on next pages

8. 3,4,5
2,3,4
4,5,7
1,1,3
2,4,7
2,3,8
Examples that work: 3,4,5 4,2,3 5,7,4
Examples that don’t work: 1,1,3 2,4,7 2,3,8

9. If the sum of two side lengths is less than the third length, no triangle can be constructed.
In no case can a given set of side lengths be used to make two different triangle shapes.
If the sum of two proposed side lengths is less than the third proposed length, no triangle can be constructed.
In no case can a given set of side lengths be used to make two different triangle shapes.
Responses will vary.
Responses will vary.

10. because the sum of any two sides is greater than the third.
What summary statement would help someone who is not here today know how to judge whether
three lengths will make a triangle
without actually building the triangle?
For example: , 3, 5 8, 2, 12 8, 8, 4
Which sets form a triangle? Why?
4, 3, 5 and 8, 8, 4
because the sum of any two sides is greater than the third.
Extension: Triangle Inequality Property
If a and b represent the two shorter sides of a triangle and c represents the longest side, then a + b > c.
Do any of the triangles have special properties? Describe them.
8, 8, 4 is isosceles since it has two equal sides. 4, 3, 5 is a right triangle because it has one 90 degree angle and is a scalene triangle since all sides have different lengths.

11. Investigation 2 : The Angle Connection
SD 3.1 Building Triangles
Did I reach my Learning Target?
I can identify what side lengths make a triangle.
Homework: Day 2 SD 3.1 Complete p. 7 and CORRECT with the KEY