In ABC , cos B = 3/25 and angle A is 90 degrees. What is cos C?
Since cos B = b / a and cos B = 3 / 25, b = 3 and a = 25 (or some multiple).
Since c2 + b2 = a2, c2 + 32 = 252 ---> c2 + 9 = 625 ---> c2 = 616 ---> c = sqrt(616).
Since cos C = c / a, cos(C) = sqrt(616) / 25