Question

how can you know what segment lenghts create a triangle

Answer 1

how many sides a triangle has ?

Answer 2

The sum of any two sides must always be greater than or equal to the third side. If the sum of any two sides is less than the third side, then no triangle is possible.

Answer 3

Take a = 1, b = 3, c = 7 for example.

1 + 3 = 4 but 4 < 7 so those lengths cannot create a triangle.

Answer 4

a = 3, b = 5, c = 7 can however since

3 + 5 > 7
5 + 7 > 3
3 + 7 > 5