1. The problem is to classify a triangle by its sides based on the given markings. 2. Triangles can be classified by their sides as follows: - Equilateral: All three sides are equal. - Isosceles: Exactly two sides are equal. - Scalene: All three sides are different. 3. The triangle shown has two sides marked with double red lines, indicating these two sides are equal. 4. The third side is marked with a single red line, indicating it is different from the other two. 5. Since exactly two sides are equal and one is different, the triangle is isosceles but not equilateral. Final answer: The triangle is **isosceles but not equilateral**.