what is the best option to verify sec(y)cos(y)=1

Question

options

 

a. cot u =sin (u)/cos(u)

b. sec(-u)=sec(u)

c. 1+tan^2(u)=sec^2(u)

d.cos (u)=1/sec(u)

 

Answer 1

Just recall the definition of secant:

 

sec(y) = 1 / cos(y)

 

So sec(y)cos(y) = [1 / cos(y)] * cos(y) = 1

 

The best answer is (d).

Answer 2

d. It is one of the identities/definitions.