Take a look at the following proof.
We're going to try to prove that if is a point inside , then .
First join and .
From the triangle inequality,
Subtract from to get,
Switch sides to get,
Here are some comments about the proof.
. The proof is not correct. There's an invalid move hiding in there somewhere.
. Relax! Not everything in this set is a trick question. This proof is perfectly fine.
. Forget the proof! The claim itself is not true!
Which comment here is correct?
This problem is from the set "MCQ Is Not As Easy As 1-2-3". You can see the rest of the problems here.