A -18 Degree Angle (9/30/14)

I was in a collaboration meeting this morning with the rest of the 8th grade teachers and before the meeting I was putting some problems together for my geometry class to work on. I made an angle chasing problem involving a triangle and a couple parallel lines, but I didn’t feel like making up equations for unknown angles, so I opened up our textbook, pulled out a couple equations that I knew had integer answers from two different problems, and just wrote them into a couple of the missing angles. When I got back to my class I glanced at the problems to see how students did with them and was immediately shocked to see that they had labeled one of the angles in the diagram as having a measure of -18 degrees. Confused, I did the calculations in my head for that part of the diagram (which involved a straight angle made up of 3 adjacent angles) and discovered that one of the equations I pulled resulted in one of the angles being 135 degrees, and another being 63 degrees, which of course, would mean that the third angle had a measure of -18 degrees. WHOOPS! I couldn’t help but start laughing. I can only imagine my class, with a substitute in the room, when they discovered this. I’m sure they were incredibly confused and tried the problem a bunch of times, sure that they were doing it right but not sure why their answer was off. I owe them an apology when I see them again on Thursday. I’m sure some of them were mad at me, but I definitely got a good laugh out of it.


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