Geometry

Question Analysis  

The main focus is using co-function identities and angle reduction for a QII angle  (since  <  < ) to express  as a cosine term.  

 

Key Concept Explanation  

Co-function identity:  for acute . For obtuse , use  (where  is the reference angle) first, then apply the identity to .  

 

Step-by-Step Solution  

1. Find the reference angle for :  

Thus, .  

2. Apply the co-function identity to :  

3. Simplify the expression:  

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