The definition of concave is a curved like a segment of the interior of a circle or hollow sphere.
That's a point where the curve of a graph changes from "concave upward" to "concave downward", or vice versa.
By definition a regular polygon cannot be concave. Concave polygons contain one or more interior angles that are greater than 180 degrees, and regular polygons can never have an interior degree greater than 180 degrees.
A simple polygon that is not convex is called concave, non-convex or reentrant. A concave polygon will always have an interior angle with a measure that is greater than 180 degrees.
The opposite of convex is concave. Concave shapes have an inward curve, while convex shapes have an outward curve.
This depends on your definition. One could say that circles ({p in R^n : d(p,m) = r}) are concave, while (open) disks ({p in R^n : d(p,m) < r}) are convex.
No, a regular octagon cannot be concave. By definition, a regular octagon has all sides and angles equal, and it is a convex polygon, meaning that all its interior angles are less than 180 degrees. A concave polygon, on the other hand, has at least one interior angle greater than 180 degrees, which is not possible in a regular octagon.
There is a good way to know if a polyhedra is convex. If you place the shape inside a sphere and all of the vertexes were touching the edge of the sphere, then it would be convex. If all of the vertexes didn't touch the edge, then it would be concave. How simply is that?
plano concave
Concave, because you can connect the corners from the outside.
Concave is a property of [irregular] polygons. A parallelogram cannot be concave.
no concave mirror is in shape of concave mirror
concave=in convex=out