Geometry

Question Analysis  

The primary focus is to apply the concept of complementary angles to represent  using cosine.

Key Concept Explanation  

Complementary Angles: Angles whose sum is  are complementary. In trigonometry, the co - function identity states that  and . This identity stems from the properties of right - angled triangles and the unit circle.

Step-by-Step Solution  

1. Determine the complementary angle:

Subtract  from , so .

2. Use the co - function identity:

By the identity , when

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