Respuesta :

add all of them then subtract from 180
check the picture below.  Notice that we can always solve for the cosine and simply use the sides alone to get an angle.

[tex]\bf cos^{-1}\left(\cfrac{10^2+(\sqrt{604})^2-18^2}{2(10)(\sqrt{604})} \right)=\measuredangle C \\\\\\ cos^{-1}\left(\cfrac{100+604-324}{20\sqrt{604}} \right)=\measuredangle C \\\\\\ cos^{-1}(0.77309903583)\approx \measuredangle C\implies 39.366998916677^o\approx \measuredangle C[/tex]
Ver imagen jdoe0001