Sample Question #149 (mathematics – geometry)

How do you prove that the three angles of a triangle always add up to 180 degrees?

(Comment: this kind of question, seemingly trivial and irrelevant, is usually employed to test two things: how you react to such a "strange" question — have you become nervous, antsy, sweaty? — and how you approach the solution, assuming you don’t remember the textbook answer any more)

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ANSWER

There’re many ways to prove this. Check out this link for one proof:

http://www.mathsrevision.net/gcse/pages.php?page=17