11多选题6★★★★☆
f(x)=alnx+bx+cx2f(x) = a\ln x + \frac{b}{x} + \frac{c}{x^2} (a0a \ne 0) 既有极大值也有极小值, 则 ( )
A.
bc>0bc > 0
B.
ab>0ab > 0
C.
b2+8ac>0b^2 + 8ac > 0
D.
ac<0ac < 0
答案与解析

答案已隐藏