The vertices of a triangle are `A(1,1),\ B(4,5)a n d\ C(6, 13)dot` Find `Cos\ Adot`

Explanation

To find \( \cos A \) for the triangle with vertices \( A(1, 1) \), \( B(4, 5) \), and \( C(6, 13) \), we will follow these steps:

### Step 1: Calculate the lengths of the sides of the triangle.

1. **Length of side \( AB \)**:
\[ AB = \sqrt{(4 - 1)^2 + (5 - 1)^2} = \sqrt{3^2 + 4^2} = \sqrt{9 + 16} = \sqrt{25} = 5 \]
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