A cosine of A that's just a standard trigonometric identity and we, in the trigonometric, less we prove that identity i think we do it multiple times then out on front we have our coefficients till we have a over c times this plus c over a times this now is there anything we can do and remember in the back of our mind we should be thinking of how can we use this information that be is equal to sixty so if we can somehow put this in the form got a b here when i think about how do you get a b here I think well you know we have a triangle here so the things that relate the sides of the triangle when especially when it's not a right triangle we are really gonna deal with the law of sines or law of cosines and a law of sines let me just rewrite it over here just for our reference
A โคไซน์ของ A นั่นก็คือสมบัติตรีโกณมิติธรรมดา