• Acute-angled Triangle: All three interior angles are acute (less than 90^).

Step 3: Types of Triangles based on angles.

• Acute-angled Triangle: All three interior angles are acute (less than $90^\circ$).
• Right-angled Triangle: One of the interior angles is exactly $90^\circ$. The side opposite the right angle is called the hypotenuse, which is the longest side.
• Obtuse-angled Triangle: One of the interior angles is obtuse (greater than $90^\circ$). The other two angles must be acute.