Finding third side of triangle using law of cosine. python

Question

For some reason the answer I get in the program is 7.091341682475861 It is supposed to be 6.66634. Can someone please explain to me what I am doing wrong. The equation is fairly simple and straightforward?

import math as mt
 def third_side(a, b, c):
                return mt.sqrt((a * a) +
                       (b * b) - 2 * a * b * mt.cos(c))
            c = 37
            a, b = 8, 11
            print(third_side(a,b,c))