I got into an argument with a mathematics grad student about the law of sines. He said that he has proven it to be wrong several times. I don't see how this is possible, given that the angles are opposing the sides, it doesn't seem possible for it to be EVER incorrect. I asked him to prove it for me but he said he didn't have time. Does anyone know about this being invalid? In my years of studying engineering, I have NEVER found the law of sines to give me a false answer.