由万能公式：sinα=[2tan(α/2)]/{1+[tan(α/2)]^2}cosα=[1-tan(α/2)^2]/{1+[tan(α/2)]^2}得:sin(2α)=2tanα/(1+tan²α)=-8/17cos(2α)=(1-tan²α)/(1+tan²α)=-15/171) sin²α=[1-cos(2α)...