[tex]\Large\boxed{\begin{array}{l}\underline{\rm Cosseno~da~soma}\\\sf cos(a+b)\\\sf =cos(a)\cdot cos(b)-sen(a)\cdot sen(b)\end{array}}[/tex]
[tex]\Large\boxed{\begin{array}{l}\sf cos(140^\circ)\cdot cos(40^\circ)-sen(140^\circ)\cdot sen(40^\circ)\\\sf\implies cos(140^\circ+40^\circ)\\\sf\implies cos(180^\circ)=-1\end{array}}[/tex]
