tan(A+B)=3,tan(A-B)=5,求tan2A和tan2B的值速答

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tan(A+B)=3,tan(A-B)=5,求tan2A和tan2B的值速答
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tan(A+B)=3,tan(A-B)=5,求tan2A和tan2B的值速答
tan(A+B)=3,tan(A-B)=5,求tan2A和tan2B的值速答

tan(A+B)=3,tan(A-B)=5,求tan2A和tan2B的值速答
tan(2a)
=tan[(a+b)+(a-b)]
=[tan(a+b)+tan(a-b)]/[1-tan(a+b)tan(a-b)]
=(3+5)/(1-3×5)
=8/(-14)
=-4/7
[[2]]
tan(2b)
=tan[(a+b)-(a-b)]
=[tan(a+b)-tan(a-b)]/[1+tan(a+b)tan(a-b)]
=(3-5)/(1+3×5)
=-2/16
=-1/8