求证:tan(π/4+α)-tan(π/4-α)=2tan2α

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求证:tan(π/4+α)-tan(π/4-α)=2tan2α求证:tan(π/4+α)-tan(π/4-α)=2tan2α求证:tan(π/4+α)-tan(π/4-α)=2tan2α左式=(1+t

求证:tan(π/4+α)-tan(π/4-α)=2tan2α
求证:tan(π/4+α)-tan(π/4-α)=2tan2α

求证:tan(π/4+α)-tan(π/4-α)=2tan2α
左式=(1+tanα)/(1-tanα)-(1-tanα)/(1+tanα)
=[(1+tanα)²-(1-tanα)²]/[(1-tanα)(1+tanα)]
=(4tanα)/(1-tan²α)
=2tan2α=右式

用差角公式
tan(A-B)=(tanA-tanB)/(1+tanA*tanB)