sin=-3/5,-π/2sin=-3/5,-π/2sin=-3/5,-π/2因为sin=-3/5,-π/2所以cosa=4/5sin2a-cos2a=2sinacosa-(cos^2a-sin^2a)=2*(-3/5)*4/5-(16/25-9/25)=-31/25sin(2α)=2sinα·cosαcos(2α)=cos^2;α-sin^2
sin=-3/5,-π/2因为sin=-3/5,-π/2所以cosa=4/5sin2a-cos2a=2sinacosa-(cos^2a-sin^2a)=2*(-3/5)*4/5-(16/25-9/25)=-31/25
sin(2α)=2sinα·cosαcos(2α)=cos^2;α-sin^2