Question

sin 870*-5cos840*=
найти sin2a, если sin a=-0,8, a€lll

Answer 1

$1)sin870-5cos840=0.5-2.5=-2 \ sin870=sin(720+150)=sin150=sin(180-30) =\ =sin30= frac{1}{2}=0.5 \ \ 5cos840=5cos(720+120)=-5cos120=-5cos(180-60)= \ =5cos60=5* frac{1}{2} = frac{5}{2} =2.5$

$2)sin2a=2sinacosa=2*(-0.8)*0.6=-0.96 \ \ sina=-0.8 \ \ cosa= sqrt{1-sin ^{2} a} = sqrt{1-(-0.8) ^{2} } = sqrt{1-0.64} = sqrt{0.36} =0.6$