Answer:
Sqrt(39)/8
Step-by-step explanation:
cos = adjacent/hypotenuse
cos A = 5/8
this means adjacent of angle a is 5 and hypotenuse is 8
for cos B, adjacent will be variable x and hypotenuse is 8
now to find x, use a^2 + b^2 = c^2, which then we will use to find cos B
x^2 + 5^2 = 8^2
x^2 + 25 = 64
x^2 = 64-25 = 39
x = sqrt(39)
thus cos B = sqrt(39)/8
