+128595 21^2=13^2+29^2-2*13*29*cosA and we're trying to find angle "A"
441 = 169 + 841 - 2(13)(29) cosA
441 = 1010 - 754 cosA subtract 1010 from each side
-569 = -754 cosA divide both sides by -754
569/754 = cosA we need to use the cosine inverse, here
cos-1 (569/754) = A = about 41°
