1. **Stating the problem:** We need to categorize triangles based on their angles into three groups: triangles with all acute angles, triangles with an obtuse angle, and triangles with one right angle. 2. **Important definitions:** - An **acute angle** is less than 90 degrees. - An **obtuse angle** is greater than 90 degrees. - A **right angle** is exactly 90 degrees. 3. **Rules for triangle classification:** - A triangle with all angles less than 90° is an **acute triangle**. - A triangle with one angle greater than 90° is an **obtuse triangle**. - A triangle with one angle exactly 90° is a **right triangle**. 4. **Applying the rules to the figures:** - Triangles marked with a right-angle corner marker belong to the category "Triangles with one right angle". - Triangles with a very wide base and one angle clearly greater than 90° belong to "Triangles with an obtuse angle". - Triangles where all angles appear less than 90° belong to "Triangles with all acute angles". 5. **Summary:** - Place triangles with right-angle markers in the "one right angle" category. - Place triangles with an angle visibly larger than 90° in the "obtuse angle" category. - Place the remaining triangles with all angles less than 90° in the "all acute angles" category. This classification helps understand triangle types based on angle measures.