Question

given a triangle a=13,b=15 and a=19 possible length of c

Answer 1

How can 'a' be both 13 and 19?

Generally, given 2 sides the third side is constrained between:

Must be longer than (Longer Length less Shorter Length)
Must be shorter than (Longer Length plus Shorter Length)

Answer 2

@lili36, could you possibly draw a picture of the triangle, because there is confusion with 'a' equaling both 13 and 19.