Răspuns :
cos30= √3 / 2
cos 60= 1/2
cos (90+α)= -sin α
cos120=cos (90+30)=-sin 30= - 1/2
cos150 = cos (90+60)= - sin 60 = - √3/2
⇒cos 30 +cos60 +cos 120 +cos 150 = √3/2 +1/2 - 1/2 - √3/2 = 0
sa se calculeze cos 30 de grade + cos 60 de grade +cos 120 de grade +cos 150 de grade .
multumesc !
cos30= √3 / 2
cos 60= 1/2
cos (90+α)= -sin α
cos120=cos (90+30)=-sin 30= - 1/2
cos150 = cos (90+60)= - sin 60 = - √3/2
⇒cos 30 +cos60 +cos 120 +cos 150 = √3/2 +1/2 - 1/2 - √3/2 = 0