Where these triangles come from?

hi , i have a model with quad meshes . when i export it for ue4 , its turning to triangles in ue4 . why ?

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and why they are not smooth ? i mean press 3 thing in maya , thanks

That is what is supposed to happen. The engine automatically triangulates / tessellates all meshes. This is one good reason why it is good to work with quads when your modeling so the engine can properly triangulate them on import. This is just how the engine processes meshes, there is nothing wrong with your models.

and why they are not smooth ? i mean
press 3 thing in maya , thanks

Consider looking into smoothing groups, when you model and when you export.