Question

(cos 780°-ctg 495°) sin 225° =

Answer 1

= (cos(720 + 60) - ctg ( 540 -45)) * sin (360 - 135) =
= (cos 60 - ctg(-45)) * sin (-135) =  (cos 60 + ctg 45) * (- sin 135) =(1/2 +1) * (- sgrt2/2)=
= 3/2 * ( -sgrt2/2)=  - 3 sgrt2 / 4