Question

(cos 780 - ctg 495 ) sin 225

Answer 1

(cos780°-ctg495°)*sin225°=
=(cos(2*360°+60°)-ctg(5*90°+45°))*sin(180°+45°)=
=((cos60°+tg45°)*(-sin45°)=
=(1/2 + 1)*(-√2/2)=3/2*(-√2/2)= $- frac{3 sqrt{2} }{4}$