Answer: Choice C) 17 degrees
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Work Shown:
Apply the law of cosines
c^2 = a^2 + b^2 - 2*a*b*cos(C)
12^2 = 28^2 + 18^2 - 2*28*18*cos(C)
144 = 1108 - 1008cos(C)
144+1008cos(C) = 1108
1008cos(C) = 1108-144
1008cos(C) = 964
cos(C) = 964/1008
C = arccos(964/1008)
C = 16.991286936969 which is approximate
C = 17 degrees
Note: arccos is the same as inverse cosine.
