## Monday, January 14, 2013

### Day 80: Practice

Students were to spend the hour working on U5 WS3 dealing with the interior and exterior angles of a triangle.

I've discovered it's very hard to write questions to assess proficiency on the Exterior Angle Theorem. In most cases, students can work through the problem using the interior angles and a linear pair. The one true problem involves representing the exterior angle with an algebraic expression (such as {x-25}deg), doing the same for one of the opposite interior angles, and then giving a measurement for the second opposite interior angle.

Students often struggle with the idea of an algebraic expression representing the angle. They'll very often pull out the x and use it alone as a representation of the angle (instead of the whole {x-25}deg). Additionally, if they do manage to solve for x, it's hard to get them to understand why they're not done, and that they need to substitute x back into the expression and then solve for the angle measure.

Those hurdles have more to do with student proficiency in algebra than in geometry, so I try very hard to separate the two aspects while grading, and SBG helps a lot with that. I promise every student that if they can set up the problem correctly, but never managed to do any algebra, they'll pass the class (with a D). That idea got a lot of them attempting more problems than before, so I hope it's momentum that will continue into the second semester.