x+y=π=4 所以tan(x+y)=tanπ/4=1=(tanx+tany)/(1-tanx*tany)
推出tanx+tany=1-tanxtany
(1+tanx)(1+tany)=1+tanxtany+tanx+tany=1+1-tanxtany+tanxtany=2
x+y=π=4 所以tan(x+y)=tanπ/4=1=(tanx+tany)/(1-tanx*tany)
推出tanx+tany=1-tanxtany
(1+tanx)(1+tany)=1+tanxtany+tanx+tany=1+1-tanxtany+tanxtany=2