using the law of cosines:
a^2 = b^2 + c^2 - 2*b*c*cos(A)
a = 90, b = 55, c = 50
90^2 = 55^2 + 50^2 - 2*55*50*cos(A)
8100 = 3025 + 2500 - 5500 * cos(A)
5500 * cos(A) = 3025 + 2500 - 8100
5500 * cos(A) = -2575
cos(A) = -103/220
A = arccos(-103/220)
A = 117.9 degrees
