30. 设函数f(x)={−x, x⩽0x2, x>0f(x)=\left\{\begin{array}{l}{-x,\;\;x\leqslant 0}\\ {{x}^{2},\;x>0}\end{array}\right.f(x)={−x,x⩽0x2,x>0，若f(α)=9f(\alpha )=9f(α)=9，则α=\alpha =α=___−9-9−9[或3 ]．