"It looks like a right angle" doesn't fly here. The Right Way to Use GDZ

Open the GDZ and look only at the first two steps of the proof. Close it and try to finish the rest yourself.

Sometimes GDZ offers a long way, and you found a short way. Understanding why both work is the key to mastery. Top Resources for Advanced Geometry

Visual clarity is essential for 3D geometry (stereometry).

Adding lines or circles that aren't there.