Online Geometry
Problem 2. Triangle, Angles, Auxiliary Lines, 20-80
Degrees.
Level: High School, Honors Geometry, College,
Mathematics Education
Prove the following: if, in a triangle
ABC, angle BAO = angle OAC = 20°, angle ACO = 10°,and angle
OCB = 30°, then angle
OBC = 80°. Try to use elementary geometry (Euclid's Elements.)