An identity is an equation that is true for all values of the variable. Some basic identities are:
To prove that an identity is true: change either side, or both sides, until the sides are the same.
I would work with the right side. Try to get it to look like the left side. Change cot
to sin and cosine s.
You have now proved the identity!
sec - sec
I would work with the left side. Factor out a sec .
sec (1 - sin2 ) = cos
Since sin2 + cos2 = 1,
So, sec (cos2 ) = cos