当x < 0时
-x > 0
所以f(-x) = (-x)² + 2x
= x² + 2x
因为y=f(x)是奇函数
所以f(x) = -f(-x) = -x²-2x
综上:f(x) = x²-2x x≥0
= -x²-2x x 0
= 0 x = 0
= -1 x < 0
当x < 0时
-x > 0
所以f(-x) = (-x)² + 2x
= x² + 2x
因为y=f(x)是奇函数
所以f(x) = -f(-x) = -x²-2x
综上:f(x) = x²-2x x≥0
= -x²-2x x 0
= 0 x = 0
= -1 x < 0