Geometry

Question Analysis

This question focuses on applying trigonometric functions in a right - triangle. The main task is to determine the correct trigonometric ratio to find the length of side  given an angle and the length of the hypotenuse.

Key Concept Explanation

In a right - triangle:

Step - by - Step Solution

We have a right - triangle  with , the hypotenuse , and the side we want to find,  (i.e., ), is the side adjacent to the  angle.

Using the cosine function, since , substituting , , and , we get