由条件推出tan(α+π/5)=-msin(α+π/5)=-mcos(α+π/5)原式=/ =/ =/ =<-mcos(π/5+α)+3cos(α+π/5)>/<-mcos(4π/5-α)-cos(α+π/5)> =(-m+3)/(-m-1) =(m-3)/(m+1)