已知tanx=- (2分之1),则sin^2x+3sin^2xcosx-1=

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已知tanx=-(2分之1),则sin^2x+3sin^2xcosx-1=已知tanx=-(2分之1),则sin^2x+3sin^2xcosx-1=已知tanx=-(2分之1),则sin^2x+3si

已知tanx=- (2分之1),则sin^2x+3sin^2xcosx-1=
已知tanx=- (2分之1),则sin^2x+3sin^2xcosx-1=

已知tanx=- (2分之1),则sin^2x+3sin^2xcosx-1=
tanx=-1/2
sinx/cosx=-1/2
cosx=-2sinx
代入:sin²x+cos²x=1
5sin²x=1
sin²x=1/5
sin²x+3sinxcosx-1
=sin²x-6sin²x-1
=-5sin²x-1
=-5*1/5-1
=-2