若tanx=1/2,tan(x-y)==-2/5,则tan(2x-y)

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若tanx=1/2,tan(x-y)==-2/5,则tan(2x-y)
若tanx=1/2,tan(x-y)==-2/5,则tan(2x-y)

若tanx=1/2,tan(x-y)==-2/5,则tan(2x-y)
tan(2x-y)
=[tanx+tan(x-y)]/[1-tanxtan(x-y)]
=(1/10)/(1+1/5)
=1/12