Resposta :
[tex]\boxed{\begin{array}{l}\sf cos(205^\circ)=cos(180^\circ+25^\circ)\\\sf cos(205^\circ)=cos(180^\circ)\cdot cos(25^\circ)- sen(180^\circ)\cdot sen(25^\circ)\\\sf cos(205^\circ)=-1\cdot0,9-0\cdot0,42\\\sf cos(205^\circ)=-0,9\end{array}}[/tex]