I believe the fewest number of sides in a planar, non-convex polygon is four.
Take any two points on or inside a body. If every point on the straight line joining the two points lies within the shape, then it is convex. If not, it is non-convex.
A non-example of a triangle is a shape that does not have three sides or three angles. For instance, a square or a circle would be non-examples, as a square has four sides and a circle has no sides at all. Additionally, a shape like a line segment, which has only two endpoints and no enclosed area, also qualifies as a non-example of a triangle.
A non convex is a concave and a convex is differently shaped
The shape that has no diagonals is a triangle. A triangle consists of three sides and three vertices, and since a diagonal connects non-adjacent vertices, there are no such connections in a triangle. Therefore, it does not have any diagonals.
A scalene triangle has three unequal sides An equilateral triangle has three equal sides
Take any two points on or inside a body. If every point on the straight line joining the two points lies within the shape, then it is convex. If not, it is non-convex.
Any non-equilateral triangle.
A shape where when you take any two points in the shape the line connecting them will be totally in the shape.
A non convex is a concave and a convex is differently shaped
irregular
A quadrilateral?
Any shape that has not got 4 sides is a non-quadrilateral
A circle is non-polygon. Meaning it has a curved side. A circle has no sides. It is non-regular.
A scalene triangle has three unequal sides An equilateral triangle has three equal sides
A shape with four non-parallel sides is an irregular quadrilateral. If the quadrilateral is bilaterally symmetrical, it is a deltoid (kite shape).
It could be an isosceles right triangle, or it could be a non-regular specimen of any polygon with more than three sides.
A convex polygon is one with no angle greater than 180 degrees. A non-convex polygon is one that is not without such an angle.