Why is there different shading on the same material I’ve been learning blender and am currently modeling my phone for practice. I have two problems, which I suspect both have to do with shading, and have thus placed them in one post. 


One of the triangles in the glass is randomly lighter than the surrounding area, and there are no defined edges along it.
The center polygons of the phone’s bottom edge are not being shaded (I think?) correctly. The whole bottom edge is the same material and is all smoothly shaded.


Pictures:


Any advice would be greatly appreciated, thanks everyone!
For the flat faces:


Select the flat faces in edit mode and set shading to smooth
Check your auto-smooth settings (under Mesh properties -> Normals)


For the other face, It looks like you have an N-gon (a face with more than 4 edges). N-gons tend to triangulate poorly and so can lead to shading artifacts, particularly when they are not convex like the one you have. You need to break this up into simpler faces.