Geometry

Question Analysis:
This question involves understanding the angle - sum property of triangles and the properties of equilateral triangles.
The main focus is to first find the unknown angle in the right - triangle and then use that to determine the type of the other triangle and find the value of .

Key Concept Explanation:
- Angle - sum property of a triangle: The sum of the interior angles of a triangle is .
- Equilateral triangle properties: A triangle with all three angles equal (each ) is an equilateral triangle, and in an equilateral triangle, all three sides are equal.

Step - by - Step Solution:
1. Find the third angle in the right - triangle:
  - In the right - triangle (the triangle on the right side of the figure), one angle is and another is .
Using the angle - sum property of a triangle (), the third angle is

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