Discovering the sum of the angles of a triangle

Discussion in 'General Education' started by Aliceacc, Sep 27, 2010.

Joined:
Apr 12, 2006
Messages:
27,534
6

Sep 27, 2010

3. mom2mikeyCohort

Joined:
Aug 16, 2009
Messages:
550
0

Sep 27, 2010

You can also draw and cut out a bunch of differnet triangles and then "rip" off each corner and discover that they will always form a straight line (180 degree angle) when you place them side by side by side.

Joined:
Feb 8, 2010
Messages:
23
0

Sep 27, 2010

5. AliceaccMultitudinous

Joined:
Apr 12, 2006
Messages:
27,534
6

Sep 27, 2010

I proved it today in class using alternate interior angles.

But this was a whole lot more visual for kids who like to actually SEE it.

Joined:
Nov 22, 2009
Messages:
3,094
0

Sep 27, 2010

That's how I've seen it done as well. It's really cool because, no matter what size or dimensions they make the triangle, when the "corners" are ripped or cut off, they will always make a straight line.

The other model is very cool as well. Thanks for finding that, Alice. :thumb:

7. BumbleGroupie

Joined:
Aug 16, 2008
Messages:
1,225
1

Sep 27, 2010

Thank you! This will help our upper grades.

8. Marci07Devotee

Joined:
Jun 2, 2008
Messages:
1,017
0

Sep 28, 2010

Isn't teaching geometry great? I love teaching geometry. It's so much fun.

Joined:
Jan 15, 2008
Messages:
3,888
0

Sep 28, 2010

Wow!

10. MissJillCohort

Joined:
Jul 30, 2009
Messages:
733
1

Sep 28, 2010

That's what I have done in the past, works great!

11. CindyBlueCohort

Joined:
Mar 24, 2004
Messages:
507
22

Sep 29, 2010

How'd you do this?? Sounds great!

12. AliceaccMultitudinous

Joined:
Apr 12, 2006
Messages:
27,534
6

Sep 29, 2010

Draw a line parallel to the base of the triangle, through the other vertex.

Then mark off the congruent alternate interior angles, one to the first vertex of the triangle, and another to the second.

Now add the 3 angles near that top vertex-- they add up to a straight angle.