Tegu r {\displaystyle r} l {\displaystyle l} Pitagoro teoremą :
r 2 = a 2 + l 2 4 {\displaystyle r^{2}=a^{2}+{\frac {l^{2}}{4}}} tada
a = r 2 − l 2 4 {\displaystyle a={\sqrt {r^{2}-{\tfrac {l^{2}}{4}}}}} Taisyklingojo n- kampio apotemos ilgis l {\displaystyle l}
a = l 2 tan 180 ∘ n {\displaystyle a={\frac {l}{2\,\tan {\frac {180^{\circ }}{n}}}}} Skirtingiems n {\displaystyle n}
Taisyklingasis Kraštinės ilgis Apotema Paviršius trikampis l = r ⋅ 3 {\displaystyle l=r\cdot {\sqrt {3}}} a = r ⋅ 1 2 {\displaystyle a=r\cdot {\tfrac {1}{2}}} A = r 2 ⋅ 3 3 4 {\displaystyle A=r^{2}\cdot {\tfrac {3{\sqrt {3}}}{4}}} kvadratas l = r ⋅ 2 {\displaystyle l=r\cdot {\sqrt {2}}} a = r ⋅ 1 2 2 {\displaystyle a=r\cdot {\tfrac {1}{2}}{\sqrt {2}}} A = r 2 ⋅ 2 {\displaystyle A=r^{2}\cdot 2} penkiakampis l = r ⋅ 1 2 ( 5 − 5 ) {\displaystyle l=r\cdot {\sqrt {{\tfrac {1}{2}}(5-{\sqrt {5}})}}} a = r ⋅ 1 4 ( 1 + 5 ) {\displaystyle a=r\cdot {\tfrac {1}{4}}(1+{\sqrt {5}})} A = r 2 ⋅ 5 8 ( 10 + 2 5 ) {\displaystyle A=r^{2}\cdot {\tfrac {5}{8}}{\sqrt {(10+2{\sqrt {5}})}}} šešiakampis l = r {\displaystyle l=r\,} a = r ⋅ 1 2 3 {\displaystyle a=r\cdot {\tfrac {1}{2}}{\sqrt {3}}} A = r 2 ⋅ 3 2 3 {\displaystyle A=r^{2}\cdot {\tfrac {3}{2}}{\sqrt {3}}} aštuonkampis l = r ⋅ 2 − 2 {\displaystyle l=r\cdot {\sqrt {2-{\sqrt {2}}}}} a = r ⋅ 1 2 + 1 4 2 {\displaystyle a=r\cdot {\sqrt {{\tfrac {1}{2}}+{\tfrac {1}{4}}{\sqrt {2}}}}} A = r 2 ⋅ 2 2 {\displaystyle A=r^{2}\cdot 2{\sqrt {2}}} n {\displaystyle n} l = r ⋅ 2 ⋅ sin 180 ∘ n {\displaystyle l=r\cdot 2\cdot \sin {\tfrac {180^{\circ }}{n}}} a = r ⋅ cos 180 ∘ n {\displaystyle a=r\cdot \cos {\tfrac {180^{\circ }}{n}}} A = r 2 ⋅ n 2 ⋅ sin 360 ∘ n {\displaystyle A=r^{2}\cdot {\tfrac {n}{2}}\cdot \sin {\tfrac {360^{\circ }}{n}}} n → ∞ {\displaystyle n\to \infty } l → 0 {\displaystyle l\to 0} a → r {\displaystyle a\to r} A → r 2 ⋅ π {\displaystyle A\to r^{2}\cdot \pi }