11. use ∆abc to find the value of cos b. 21. use ∆abc to find the value of tan b.(shorter one is number 11)

The first thing we are going to do for this case is to define the cosine and the tangent:
 For the cosine we have:
 
 Where,
 C.A: adjacent leg
 h: hypotenuse
 On the other hand we have that the tangent is given by:
 Where,
 
 Where,
 C.O: opposite leg
 C.A: adjacent leg
 We have then:
 
 Part A
 
 Simplifying:
 

 Part B