Answer:
See Explanation
Step-by-step explanation:
<em>Question like this are better answered if there are list of options; However, I'll simplify as far as the expression can be simplified</em>
Given

Required
Simplify

Represent  with a
 with a
Represent  with b
 with b
The expression becomes

Factorize



Recall that 
  
 

The expression  becomes
 becomes

..............................................................................................................................
In trigonometry

Subtract  from both sides
 from both sides


..............................................................................................................................
Substitute 1 for  in
 in 

Open Bracket
 ------------------This is an equivalence
 ------------------This is an equivalence

Solving further;
................................................................................................................................
In trigonometry


Substitute the expressions for secx and tanx 
................................................................................................................................
 becomes
 becomes

Open bracket


Add Fraction
 ------------------------ This is another equivalence
 ------------------------ This is another equivalence
................................................................................................................................
In trigonometry

Make  the subject of formula
 the subject of formula

................................................................................................................................
Substitute the expressions for  for
 for 

Open bracket

 ---------------------- This is another equivalence
 ---------------------- This is another equivalence