题库网
#421ed568-5db3-4e98-b2a1-2b65187e22ff中等解答题恒成立与端点效应导数

8.(2023春•东城区校级月考)设函数f(x)=x(x23x+a)f(x)=x(x^{2}-3x+a)aRa\in R
(1)当a=9a=-9时,求函数f(x)f(x)的单调增区间;
(2)若函数f(x)f(x)在区间(1,2)(1,2)上为减函数,求aa的取值范围;
(3)若函数在区间(0,2)(0,2)内存在两个极值点x1x_{1}x2x_{2},且f(x1)f(x2)>f(x1)+f(x2)\vert f(x_{1})-f(x_{2})\vert >\vert f(x_{1})+f(x_{2})\vert,求aa的取值范围.