А) 2cos п/6 - 4 sin п/3 + cos 360° б) cos 780° в) sin 4п/3 ,

A) 2cos pi/6 - 4sin pi/3 + cos 360° = 2*√3/2 - 4*√3/2 + 1 = √3 - 2√3 + 1 = 1 - √3 b) cos 780° = cos (720° + 60°) = cos (2*360° + 60°) = cos 60° = 1/2 c) sin 4pi/3 = sin (pi + pi/3) = -sin pi/3 = -√3/2

cos(a)=ac/ab

 

ac=ab*cos(a)=5*0,8=4

 

bc^2=ab^2-ac^2

bc^2=5^2-4^2=25-16=9

dc=3