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To determine which sets of lengths can form a triangle, you should apply the triangle inequality theorem. This theorem states that the sum of the lengths of any two sides of a triangle must be greater than the length of the third side. Let's evaluate each option: 1. **9 см, 18 см, 15 см** - 9 + 18 > 15 - 9 + 15 > 18 - 18 + 15 > 9 - All conditions are satisfied. 2. **21.5 см, 6 см, 15 см** - 21.5 + 6 > 15 - 21.5 + 15 > 6 - 6 + 15 = 21, which is not greater than 21.5 3. **18.5 см, 25.5 см, 39.5 см** - 18.5 + 25.5 = 44, which is greater than 39.5 - 18.5 + 39.5 > 25.5 - 25.5 + 39.5 > 18.5 - All conditions are satisfied. 4. **29.5 см, 5 см, 45 см** - 29.5 + 5 = 34.5, which is not greater than 45 5. **15 см, 15 см, 15 см** - 15 + 15 > 15 - This is an equilateral triangle, and therefore valid. 6. **6 см, 5 см, 15 см** - 6 + 5 = 11, which is not greater than 15 7. **16 см, 10 см, 32 см** - 16 + 10 = 26, which is not greater than 32 The valid sets of lengths that can form a triangle are: - 9 см, 18 см, 15 см - 18.5 см, 25.5 см, 39.5 см - 15 см, 15 см, 15 см