Septiņstūris - daudzstūris ar septiņām malām. Septiņstūra leņķu summa ir 900°. Tam ir 14 diagonāles. Katrs regulāra septiņstūra leņķis ir aptuveni 128,57° liels.
Laukums
S
=
7
4
⋅
a
2
⋅
tan
450
∘
7
≈
3,633
91
⋅
a
2
{\displaystyle S={\frac {7}{4}}\cdot a^{2}\cdot \tan {\frac {450^{\circ }}{7}}\approx 3{,}63391\cdot a^{2}}
S
=
7
2
⋅
R
2
⋅
sin
360
∘
7
≈
2,736
41
⋅
R
2
{\displaystyle S={\frac {7}{2}}\cdot R^{2}\cdot \sin {\frac {360^{\circ }}{7}}\approx 2{,}73641\cdot R^{2}}
riņķa līnijas rādiuss
S
=
7
4
a
2
ctg
π
7
{\displaystyle S={\frac {7}{4}}a^{2}\operatorname {ctg} {\frac {\pi }{7}}}
S
=
7
2
R
2
sin
2
π
7
{\displaystyle S={\frac {7}{2}}R^{2}\sin {\frac {2\pi }{7}}}
S
=
7
r
2
tg
π
7
{\displaystyle S=7r^{2}\operatorname {tg} {\frac {\pi }{7}}}
Perimetrs
P
=
7
a
=
14
R
sin
π
7
=
14
r
tg
π
7
{\displaystyle P=7a=14R\sin {\frac {\pi }{7}}=14r\operatorname {tg} {\frac {\pi }{7}}}
a
=
2
R
sin
π
7
=
2
r
tg
π
7
;
r
=
R
cos
π
7
{\displaystyle a=2R\sin {\frac {\pi }{7}}=2r\operatorname {tg} {\frac {\pi }{7}}~;~r=R\cos {\frac {\pi }{7}}}
a
=
2
⋅
R
⋅
sin
180
∘
7
≈
R
⋅
0,867
767478235
{\displaystyle a=2\cdot R\cdot \sin {\frac {180^{\circ }}{7}}\approx R\cdot 0{,}867767478235}
