12. A/an triangle has all three angles measuring less than 90°. A. acute B. scalene C. obtuse D. right

Break Down the Problem

1. Identify the types of triangles based on their angles.
2. Determine which type of triangle has all angles less than 90°.

Relevant Concepts

• Acute Triangle: A triangle where all angles are less than 90°.
• Scalene Triangle: A triangle with all sides of different lengths, which can be acute, obtuse, or right.
• Obtuse Triangle: A triangle with one angle greater than 90°.
• Right Triangle: A triangle with one angle equal to 90°.

Analysis and Detail

• From the definitions, only the acute triangle meets the requirement of having all angles measuring less than 90°.
• Scalene does not specify anything about angles; it only refers to side lengths.
• Obtuse and right triangles have angles that are either greater than or equal to 90°.

Verify and Summarize

Based on the definitions, we can conclude that the triangle with all angles less than 90° is specifically an acute triangle.

Final Answer

A. acute