Geometry

Question Analysis  

The main focus is to use angle reduction for obtuse angles and co-function identities to express in terms of sine, considering its quadrant (QII) where cosine is negative.  

Key Concept Explanation  

Co-function identity: (for acute ).  

Angle reduction for QII: when is in QII ( < < ).  

Step-by-Step Solution  

1. Reduce to an acute angle:  

2. Apply the co-function identity to :  

Click "Show Answer" to reveal the answer and analysis