How can you use a right angle to determine the classification of another angle

Answer 1

A triangle has 180 degrees. A right angle measures 90 degrees. Therefore each of the other angles adds up to less than 90 degrees.

http://www.algebralab.org/lessons/lesson.aspx?file=Geometry_AnglesAcuteRightObtuse.xml

Answer 2

A triangle has 180 degrees