**The
Angle **

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

**Approaches**

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*