Question

Given the right triangle ABC, with C the right angle and legs AC and BC measuring 6 and 8, respectively, what is cos B?

Answer 1

Given that the formula is Cos θ = adj/hyp. We cannot apply the formula until we know what is the length of the hypotenuse. 

To find hypotenuse, we will use the Pythagoras theorem:

a² + b² = c²

Substitute a = 6 and b = 8, we will be able to find c.

6² + 8² = c²
c² = 36 + 64
c² = 100
c = √100
c = 10

Now that we know that the hypotenuse is 10 units, we can find cos B:

Cos B = adj/hyp
Cos B = 8/10
Cos B = 4/5

----------------------------------------------
Answer: Cos B = 4/5
----------------------------------------------