Plane shapes consist of the basic building blocks of geometry, which we learned in the chapter Geometry - geometric shapes. Geometric shapes are also called geometric figures.
A geometric figure is a set of points in a plane bounded by a closed curve that does not intersect itself.
In addition to plane shapes, we also know solid shapes, in which the sides can intersect, but their treatment exceeds the content of this subject matter, so they are not covered in this textbook.
Plane shapes are divided into polygons and other shapes.
A polygon is a plane figure enclosed by line segments called sides.
Polygons include:
hexagon
Other n-angle plane shapes.
The points of a broken line segment are called vertices of a geometric figure, and the sections between successive vertices are called sides of a geometric figure.
We mark the corners in capital letters, the sides and their lines in small letters.
A special case of polygons is regular polygon. It is characterized by the fact that all sides are of equal length and all angles are equal.
Polygons are divided into convex and concave.
For convex polygons, it holds that:
each internal angle is less than or equal to 180°
each line between two vertices is located inside or on the edge of the polygon
The figure shows a convex quadrilateral:
Convex quadrilateral
For concave polygons, it holds that:
at least one interior angle is greater than 180° (in the case of a quadrilateral exactly one interior angle)
there is a line between two vertices, part of which is located outside the polygon
The figure shows a concave quadrilateral:
Concave Quadrilateral
These figures are bounded by uneven border lines.
The most important of these is the circle, which is described by the distance from the center to the circumference of the circle, ie radius r:
