利用tan（α+β）= (tanα + tanβ)/(1-tanα*tanβ)tan（α-β）= (tanα - tanβ)/(1+tanα*tanβ) tan2α = tan[(α+β)+(α-β)]= [tan(α+β) + tan(α-β)]/[1-tan(α+β)*tan(α-β)] = (3 + 5)/(1-3*5...