1. **Problem:** Describe a triangle. 2. A triangle is a basic shape in geometry with **3 sides**, **3 angles**, and **3 vertices**. 3. The sum of the interior angles of any triangle is always $180^\circ$. 4. Triangles can be classified in two common ways: - By sides: equilateral, isosceles, and scalene. - By angles: acute, right, and obtuse. 5. Important rules: - A triangle must have exactly 3 straight sides. - The side lengths must satisfy the triangle inequality: the sum of any two sides must be greater than the third side. - A right triangle has one angle equal to $90^\circ$. 6. In simple words, a triangle is a 3-corner shape that appears often in math, design, and real life. 7. Final answer: A triangle is a polygon with 3 sides, 3 angles, and 3 vertices.