1. **Problem Statement:** Classify the given triangle by its sides based on the markings. 2. **Understanding the markings:** The triangle has one side marked with one red line and another side marked with two red lines. These markings indicate that two sides are equal in length. 3. **Classification rules:** - An **equilateral** triangle has all three sides equal. - An **isosceles** triangle has exactly two sides equal. - A **scalene** triangle has all sides of different lengths. 4. **Applying the rules:** Since the triangle has two sides marked as equal and the third side is different (no matching mark), it is an **isosceles but not equilateral** triangle. 5. **Conclusion:** The triangle is **isosceles but not equilateral** because it has exactly two equal sides.