Which set of side lengths cannot form a triangle?

1 answer

To determine whether a set of side lengths can form a triangle, you can use the triangle inequality theorem. This theorem states that for any triangle with side lengths \(a\), \(b\), and \(c\):

  1. \(a + b > c\)
  2. \(a + c > b\)
  3. \(b + c > a\)

If any of these conditions are not met, the lengths cannot form a triangle.

For example, let's consider these sets of side lengths:

  1. \(3, 4, 5\)
  2. \(1, 1, 2\)
  3. \(5, 7, 10\)
  4. \(6, 8, 10\)

Let's apply the triangle inequality theorem to each one:

  1. \(3, 4, 5\):

    • \(3 + 4 = 7 > 5\) (True)
    • \(3 + 5 = 8 > 4\) (True)
    • \(4 + 5 = 9 > 3\) (True)
    • This can form a triangle.
  2. \(1, 1, 2\):

    • \(1 + 1 = 2\) is not greater than \(2\) (False)
    • Since one condition fails, this cannot form a triangle.
  3. \(5, 7, 10\):

    • \(5 + 7 = 12 > 10\) (True)
    • \(5 + 10 = 15 > 7\) (True)
    • \(7 + 10 = 17 > 5\) (True)
    • This can form a triangle.
  4. \(6, 8, 10\):

    • \(6 + 8 = 14 > 10\) (True)
    • \(6 + 10 = 16 > 8\) (True)
    • \(8 + 10 = 18 > 6\) (True)
    • This can form a triangle.

From this analysis, the set of side lengths \(1, 1, 2\) cannot form a triangle.