12abc\frac{1}{2} a b c21abc
3abc3 \mathrm{abc}3abc
12(a−b)(b−c)(c−a)\frac{1}{2}(a-b)(b-c)(c-a)21(a−b)(b−c)(c−a)
12(b−a)(b−c)(c−a)\frac{1}{2}(b-a)(b-c)(c-a)21(b−a)(b−c)(c−a)
