y=tanx在(-π/2,π/2)上是增函数∵y=tanwx在(-π/2,π/2)是减函数∴w<0由 -π/2得π/(2w)∴y=tanwx在原点附近的单调递减区间为 (π/(2w),-π/(2w))因此，（-π/2，π/2)是 (π/(2w),-π/(2w))的子集∴π/2≤-π/(2w)∴w≥-1综上，-1≤w<0
