Answer:
X ≈ 117.9°
Step-by-step explanation:
The law of cosines formula is given. Solving it for C, we find ...
C = arccos((a^2 +b^2 -c^2)/(2ab))
where a and b are the sides adjacent to the angle of interest.
Here, we have ...
X = arccos((50^2 +55^2 -90^2)/(2·50·55)) = arccos(-2575/5500)
X ≈ 117.9°
