Please help: some faces show a dark triangles

Hey Everyone! first of all, I apology for the bad English it’s not my natal language.

I have been trying to solve this for a few days now and I can’t seem to find anything about it, the worst of all its that I have no idea what it happened in the first place because the 3D model was handed to me

as you can see in the image above, the model shows some weird triangles in some of the faces, any idea what it’s causing it to happen?

thank you so much!

smoothing. you need to define sharp edges, or just turn it off.

As he said:

Alternatively you may add a Edge split modifier instead of defining sharp edges

if i remove the smooth option it wont go away!, the sharp edges wont fix in neither :c … thanks for the replies!

edit: i know the sharp edges modifier its not toggled, i just put it out for the screen capture