Puoliympyrä

Puoliympyrä is a Finnish term that translates to "semicircle" in English. It refers to half of a circle, formed by cutting a circle along a diameter. A semicircle is a geometric shape characterized by a curved boundary and a straight line segment (the diameter) connecting the endpoints of the curve.

The area of a semicircle is half the area of a full circle. If the radius of the circle is $r$, the area of the full circle is $\pi r^2$. Therefore, the area of a semicircle is $\frac{1}{2}\pi r^2$. The perimeter of a semicircle consists of the length of the curved arc and the length of the diameter. The arc length of a semicircle is half the circumference of the full circle, which is $\pi r$. Adding the diameter ($2r$) gives a total perimeter of $\pi r + 2r$, or $r(\pi + 2)$.

In geometry, semicircles appear in various contexts, such as in the study of arcs, sectors, and segments of circles. They can also be found in architectural designs and artistic representations. The concept of a semicircle is fundamental in understanding more complex geometric figures and calculations. Its symmetrical nature and simple definition make it a common element in mathematical problems and visual designs.