= Law of sines
{title2=$\sin A/a=\sin B/b=\sin C/c$}
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= Sine-rule
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In a nondegenerate <triangle>, let $a,b,c$ be the side lengths opposite the interior <angles> $A,B,C$. Its <area> $K$ satisfies $2K=bc\sin A=ca\sin B=ab\sin C$. Division by $abc>0$ proves the law of sines. The area formula itself follows by taking the magnitude of the <cross product> of two edge vectors. Unlike the <law of cosines>, this relation alone may leave an ambiguity between two supplementary angles when two sides and a nonincluded angle are given.
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