Ha egy trapézoidban $AB=a\mathrm{,}BC=b\mathrm{,}CD=c\mathrm{,}DA=d$, akkor
$1^{\circ }a=d\text{cos}\alpha +b\text{cos}\beta -c\text{cos}\left(\beta +\gamma \right)=d\text{cos}\alpha +b\text{cos}\beta -c\text{cos}\left(\alpha +\delta \right)$,
$2^{\circ }a\text{sin}\alpha =c\text{sin}\delta +b\text{sin}\left(\alpha +\beta \right)$,
$3^{\circ }a\text{sin}\beta =c\text{sin}\gamma +d\text{sin}\left(\alpha +\beta \right)$.