[tex]\Large\boxed{\begin{array}{l}\underline{\rm Seno~da~diferenc_{\!\!,}a}\\\sf sen(a-b)\\\sf= sen(a)\cdot cos(b)-sen(b)\cdot cos(a)\end{array}}[/tex]
[tex]\Large\boxed{\begin{array}{l}\sf sen(105^\circ)\cdot cos(75^\circ)-sen(75^\circ)\cdot cos(105^\circ)\\\sf\implies sen(105^\circ-75^\circ)\\\sf\implies sen(30^\circ)=\dfrac{1}{2}\end{array}}[/tex]
