Question 824276
You can find a reference about Law of Cosines in your Trigonometry book, and maybe in other sources.  


The angle between the 500m and the 461m side is according to this:
{{{500^2+461^2-2*500*461*cosine(alpha)=408^2}}}, and I call this angle between them to be alpha.


{{{500^2+461^2-408^2=2*500*cosine(alpha)}}}
{{{cosine(alpha)=(500^2+461^2-408^2)/(2*500)}}}
... and keep going until you find this alpha.


Use the same arrangement for every angle in this triangle.