[tex]\large\boxed{\begin{array}{l}\rm 1305^\circ|\underline{360^\circ}\\\!\!\!\!-\underline{\rm1080^\circ}~~3\\\rm\,\,\,225^\circ\\\\\rm 1305^\circ=3\cdot360^\circ+225^\circ\\\rm cos(1305^\circ)=cos(225^\circ)=-cos(45^\circ)\\\rm cos(1305^\circ)=-\dfrac{\sqrt{2}}{2}\end{array}}[/tex]
