Planimetry - practice problems

Planimetry is a branch of geometry that deals with flat (two-dimensional) figures and their properties. It studies plane measurements, including angles, distances, and areas — in other words, the measurement and calculation of shapes in a two-dimensional plane.
Planimetry focuses on plane figures such as circles, triangles, and quadrilaterals, and examines their mutual positions (perpendicularity, parallelism), metric properties (perimeter, area), and construction tasks (using a compass and straightedge).
Typical problems include finding the perimeter and area of plane shapes.

Example:
Planimetry: Calculation of the area of a circle S = π r².
Stereometry: Calculation of the volume of a sphere V = 4/3 π r³.
Planimetry is therefore the part of geometry that is limited to two-dimensional figures, as opposed to stereometry (solid geometry), which deals with three-dimensional objects.