Question 184063
If a shape that has three sides and three angles,can we call that a triangle? Generally speaking - no. In order to be a 'euclidean triangle' the sides must be line segments. (that is, they cannot be curved). See http://www.mathopenref.com/triangle.html

If the sides of the triangles are unstraight lines ,how can we call that? A 3 sided polygon.

How can I know its angles and sides by computing? I'll assume you mean on a triangle. Use the law of sines --> http://en.wikipedia.org/wiki/Law_of_sines