Which sets of three of numbers represent the sides of an obtuse triangle? Check all that apply.

For each set, first check that the two shorter sides add to more than the longest side, then compare the squares: a triangle is obtuse when the longest side squared is greater than the sum of the other two squares. For 2, 2, 3, the triangle inequality holds and 3² = 9 > 2² + 2² = 8. For 3, 5, 6, the triangle inequality holds and 6² = 36 > 3² + 5² = 34. Thus the obtuse triangles are 2, 2, 3 and 3, 5, 6.

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