Question 453942
Using the cosine rule we have:


a^2 = b^2 + c^2 - 2bc Cos A


Rearrange to have
(b^2 + c^2 - a^2)/2bc = Cos A



So if A is the angle opposite the side of length 13ft, we have a=13 and we can have b=12 and c=14. It doesn’t matter if b=14 and c=12 we get the same result a long as a=13).


(144 + 196 - 169)/336 = 171/336 = Cos A


A = 59.4 degrees