In the context of angles in standard position, which type of angle is formed by extending one side of a $\mathrm{triangle}$ beyond its vertex?

• A. An exterior angle
• B. An interior angle
• C. A straight angle
• D. A right angle

Answer: (A)

Verified step by step guidance

1. Recall the definition of an angle in standard position: it is an angle whose vertex is at the origin and one side lies along the positive x-axis.
2. Understand that in a triangle, an interior angle is formed between two sides of the triangle at a vertex.
3. When one side of the triangle is extended beyond a vertex, the angle formed outside the triangle adjacent to the interior angle is called an exterior angle.
4. Recognize that a straight angle measures 180 degrees and a right angle measures 90 degrees, but these terms describe specific angle measures rather than the position relative to the triangle.
5. Therefore, the angle formed by extending one side of a triangle beyond its vertex is known as an exterior angle.