Can you have a percent error over 100%? how would you determine it?

Yes, a percent error of over 100% is possible. A percent error of 100% is obtained when the experimental value is twice the value of the true value. In experiments, it is always possible to get values that are way greater or lesser than the true value due to human or experimental errors. 

One unique triangle, because those angles add up to 180, and that's how many degrees there are in one triangle.