Geometry

Question Analysis

This question actually involves the concept of trigonometric ratios in right - angled triangles. The main focus is to find the cosine of an angle in a right - triangle by using the appropriate side - length ratio.

 

Key Concept Explanation:

In a right - triangle, for an acute angle , .

 

Step-by-Step Solution

In right - triangle , we know that , , , .

For right - triangle which is similar to (by AA similarity since and ), the cosine of (which is equivalent to in ) is calculated as follows:

The adjacent side to is and the hypotenuse is .

Using the formula , we get

 

Option Analysis

A.

Click "Show Answer" to reveal the answer and analysis