x+y=3π/4,则(1-tanx)(1-tany)

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x+y=3π/4,则(1-tanx)(1-tany)x+y=3π/4,则(1-tanx)(1-tany)x+y=3π/4,则(1-tanx)(1-tany)(1-tanx)(1-tany)=1-(ta

x+y=3π/4,则(1-tanx)(1-tany)
x+y=3π/4,则(1-tanx)(1-tany)

x+y=3π/4,则(1-tanx)(1-tany)
(1-tanx)(1-tany)
=1-(tanx+tany)+tanxtany.(1)
因为x+y=3π/4
而且tan(x+y)=(tanx+tany)/(1-tanxtany)
tan(x+y)=tan(3π/4)=-1
(tanx+tany)/(1-tanxtany)=-1
tanx+tany=tanxtany-1.(2)
将(2)式子代入(1)式子
得(1-tanx)(1-tany)=2