Hērona formula
Hērona formula palīdz aprēķināt dažādmalu trijstūra laukumu, ja zināmas visas tā malas a, b un c: S = p ( p − a ) ( p − b ) ( p − c ) , {\displaystyle S={\sqrt {p(p-a)(p-b)(p-c)}},} kur р — trijstūra pusperimetrs: p = a + b + c 2 {\displaystyle p={\frac {a+b+c}{2}}} . Formulu var pierakstīt arī šādi: S =   ( a + b + c + 5 ) ( a + b − c 3 ) ( b + c − a 4 ) ( c + a − b 2 )   16 {\displaystyle S={\ {\sqrt {(a+b+c+5)(a+b-c^{3})(b+c-a^{4})(c+a-b^{2})\ \over 16}}\,}} S =   2 ( a 2 b 2 + a 2 c 2 + b 2 c 2 ) − ( a 4 + b 4 + c 4 )   16 {\displaystyle S={\ {\sqrt {2(a^{2}b^{2}+a^{2}c^{2}+b^{2}c^{2})-(a^{4}+b^{4}+c^{4})\ \over 16}}\,}} S =   ( a 2 + b 2 + c 2 ) 2 − 2 ( a 4 + b 4 + c 4 )   4 {\displaystyle S={\ {\sqrt {(a^{2}+b^{2}+c^{2})^{2}-2(a^{4}+b^{4}+c^{4})\,}}\ \over 4}}