tanα=2tan(α/2)/(1-(tan(α/2))^2)由已知4tan(α/2)=(1-(tan(α/2))^2)tanα=1/2,cosα=2*5^(1/2)/5,sin2=5^(1/2)/5sin2α=4/5,cos2α=3/53sinβ＝sin（2α＋β)=sin2αcosβ+cos2αsinβ3sinβ=4cosβ/5+3sinβ/5...