The Angle

How many degrees are in angle ABC? (the lines are parallel) .


It looks like a right angle.

Can you measure it or prove your conjecture?

Draw a parallel through B, add alternate interior angles.

Extend AB or CB to make triangle; ABC is exterior angle

Drop a perpendicular from A; use complements and supplements to get three angles of quadrilateral, of which ABC is the fourth angle.

Your experience

Have you used this problem with a class and seen approaches other than(or more specific than) those mentioned above? Or do you have other comments or criticisms or stories? If so, please tell us!

Last updated 30 November, 2004