# Thread: Mathematical Proof that i = r

1. I've been scouring the internet for a mathematical proof that:

the angle of incidence = the angle of reflection

and have come up fruitless.
If someone could help me out or even give me a hint as how to proove it myself i would be most obliged.

2.

3. Originally Posted by JekPorkins
I've been scouring the internet for a mathematical proof that:

the angle of incidence = the angle of reflection

and have come up fruitless.
If someone could help me out or even give me a hint as how to proove it myself i would be most obliged.
You will not find a mathematical proof.

It is not a mathematical theorem, but rather a physical principle.

Now, you can derive it from other, more fundamental physical principles (such as the principle of least time) but to do would require that you make clear what your starting point is.

http://en.wikipedia.org/wiki/Fermat's_principle

4. Maybe this will also help to shed some light on it:
http://en.wikipedia.org/wiki/Snell%27s_law

5. I thought there was a way to prove it with calculus of variations. Let me think about it... it's been a while.

6. Originally Posted by kakarot
I got no idea about the math proof!
Then why even bother to post? You are just using up bandwidth in a pointless manner. I, for one, would appreciate it if you would stop.
Please engage in threads in a meaningful way. Offer additional information. Provide an alternative point of view. Ask relevant and thoughtful questions. Even just make an amusing remark, but stop this lightweight verbal burping.

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