????????? ( ????????? : circle ) ????????? ????????????? ??? ?????? (2-dimensional) ???????? ( en:ball (mathematics) ) ??????????? ??????????? ????????? ?????????? ???????? ??????? ??????????? ??????????????????????? ??????????????????????? ?????????????? ???????? ???????????????? ????????????? ???????????? ??????????? ???? ?? ???????? ???????????? ??????????? ????????? ?? ???????? ????????? ??????????????????????? ????????? ????????? ???????????? ??????????? ?????????????? ?????????? ????????????? ??? ?????? ???????? (3-dimensional ball) ????? ??????? ???????? ????????????? ??? ?????? ???????? (1-dimensional ball) ????? ????????? ????????
????????? (radius) ? ???????? ?????? (diameter) ???????? ?????????????? ???????????????? ???????????? ????? (????) ?????????? ????????????? ??????? ?? ???????? ????? ??????? π ???????????? π ? ??????????? ??????????????????? 22 7 {\displaystyle {\frac {22}{7}}} ????????????? ??????????????????? 3.1416 {\displaystyle 3.1416} (????) 3.142 {\displaystyle 3.142} (????) 3.14 {\displaystyle 3.14} ???????????? ??????????????? ???????????? ??????????????????? R {\displaystyle R} ????????? ???????????? ?????????? C = π R {\displaystyle C={\pi }R} ????????? ????????
??????????????????? R {\displaystyle R} ????????? ????????????? ????? ???????????? r = R 2 {\displaystyle r={\frac {R}{2}}} ???????? ?????????????????? A = π r 2 {\displaystyle A={\pi }r^{2}} ????????
???????? ???????????? ??????????? (Euclidean Cartesian Coordinate System) ???????? X ????? Y ?????????????????? ?????????????? ???????????? ??????????? ???????? ??? y ( x ) = r 2 − x 2 {\displaystyle y(x)={\sqrt {r^{2}-x^{2}}}} ????????? x ( y ) = r 2 − y 2 {\displaystyle x(y)={\sqrt {r^{2}-y^{2}}}} ????????