已知f(x)=ax3+bx2+cx+d(a>0)为增函数,则(    )A.b2-4ac>0           

已知f(x)=ax3+bx2+cx+d(a>0)为增函数,则(    )

A.b2-4ac>0             B.b>0,c>0             C.b=0,c>0             D.b2-3ac<0

答案

答案:

D  f′(x)=3ax2+2bx+c>0恒成立.因为a>0,则Δ=4b2-4·3ac<0,即b2-3ac<0.

相关题目

调节人体水和无机盐平衡最重要的器官是 A.肾脏        B
调节人体水和无机盐平衡最重要的器官是 A.肾脏        B.汗腺         C.肺            D.大肠
西方有句谚语:“你可以强行把马拉到水边,但你不能强迫
西方有句谚语:“你可以强行把马拉到水边,但你不能强迫马喝水。”在中国也有“强扭的瓜不甜”的谚语。强迫马喝水和强扭瓜的行为的共同错误在
如果方程x 2+ky 2=2表示焦点在y轴上的椭圆,那么实数k的取值
如果方程x 2+ky 2=2表示焦点在y轴上的椭圆,那么实数k的取值范围是(   )     A.(0, +∞)        B.(0, 2)        C.(0, 1)        D. (1, +∞)
一个处于人工培养条件下的体细胞连续进行2次分裂,其子细
一个处于人工培养条件下的体细胞连续进行2次分裂,其子细胞的染色体数 (    ) A.减少一半                    B.为原来的1/4 C.保持不变   
如图所示,是测定电流表内阻的电路,电源内阻不计,当电
如图所示,是测定电流表内阻的电路,电源内阻不计,当电阻箱的电阻调到1200 Ω时,电流表指针偏转到满刻度;再把电阻箱的电阻调到3000 Ω时,电流表
Everybody loves a fat pay rise. Yet pleasure at your own can disappear if you le
Everybody loves a fat pay rise. Yet pleasure at your own can disappear if you learn that a colleague has been given a bigger one. Indeed, if he has a reputation for incompetence in their work, you mig
What does the word“home”mean to you? How do you say the word in French? In S
What does the word“home”mean to you? How do you say the word in French? In Spanish? In your language? Although people usually know what the word means it often has no exact translation(翻译)
12.一工厂生产了某种产品16800件,它们来自甲、乙、丙3条生
12.一工厂生产了某种产品16800件,它们来自甲、乙、丙3条生产线.为检查这批产品的质量,决定采用分层抽样的方法进行抽样.已知从甲、乙、丙3条生产

最新题目