1. Use The Law of Cosines first to calculate one of the angles 2. Then use The Law of Cosines again to find another angle 3. And finally use angles of a triangle add to 180° to find the last angle.
law of cosines:
cos(C) = (a^2 + b^2 − c^2)/2ab
cos(A) = (b^2 + c^2 − a^2)/2bc
cos(B) = (c^2 + a^2 − b^2)/2ca
