We are familiar with the formula for the area of a circle with radius \(r \), centered at a certain point, which is given by \( \pi r^2 \). However, this can be misleading.

The reason is that the definition of a circle is “the set of points equidistant from a given point⭕️.” In other words, this set represents a curve (known as the circumference), so its area would be zero.

However, in Japanese, when we refer to the “area of a circle,” we are including the inside of the circumference, called a “disk,” which allows us to measure its area.

Thus, it is necessary to be careful whether the term “circle” refers to the circumference or the disk. In English, the terms “circle” and “disk” are used distinctly to clarify this difference.