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the answers here assume that the base is a continuous, straight line
given one of the angles on the left triangle is a right angle on the diagram, but 80 if you calculate it, you can't assume that
This is a standard way to draw geometric proofs, it's not at all unreasonable to assume straight lines and unrepresentative angles.
normally in a geometric proof, a right angle is a right angle
This was certainly not my experience in high school. An unlabelled angle could never be assumed. Only angles marked with a square could be taken as right angles.
guess you're right!
137 comments