sin 390 cos 420 tg 780 ctg 405

sin 390 cos 420 tg 780 ctg 405=? sin390=sin (360+30)=sin30=1/2cos420=cos (360+60)=cos60=1/2tg780=tg (360*2+60)=tg60=sqrt{3}ctg405=ctg (360+45)=ctg45=1sin 390 cos 420 tg 780 ctg 405=1/2*1/2*sqrt{3}*1=sqrt{3}/4