Question

решите пожалуйста cos 105°+ cos 75°

Answer 1

cos105+cos75 = 2cos((105+75)/2)cos((105-75)/2) = 2cos90cos15=0

Answer 2

cos 105°+ cos 75°=cos(60+45)+cos(30+45)=cos60cos45-sin60sin45 +cos30cos45-sin30sin45=1/2*√2/2-√3/2*√2/2+√3/2*√2/2-1/2*√2/2=0

cos 105°+ cos 75°=cos(180-75)+cos75=-cos75+cos75=0