优质解答
设f(x)=x2+bx+c(x∈R),且满足f'(x)+f(x)>0.对任意正实数a,下面不等式恒成立的是( )
A.f(a)>eaf(0)B.f(a)<eaf(0)C.f(a)<f(0)eaD.f(a)>f(0)ea
令F(x)=ex×f(x),
∵f'(x)+f(x)>0
∴F′(x)=(ex)′×f(x)+ex×f′(x)
=ex×f(x)+ex×f′(x)
=ex(f'(x)+f(x))>0,
∴F(x)=ex×f(x)为增函数,又a>0,
∴F(a)>F(0),即eaf(a)>e0f(0)=f(0),
∴f(a)>
f(0)ea
.
故选D.
设f(x)=x2+bx+c(x∈R),且满足f'(x)+f(x)>0.对任意正实数a,下面不等式恒成立的是( )
A.f(a)>eaf(0)B.f(a)<eaf(0)C.f(a)<f(0)eaD.f(a)>f(0)ea
令F(x)=ex×f(x),
∵f'(x)+f(x)>0
∴F′(x)=(ex)′×f(x)+ex×f′(x)
=ex×f(x)+ex×f′(x)
=ex(f'(x)+f(x))>0,
∴F(x)=ex×f(x)为增函数,又a>0,
∴F(a)>F(0),即eaf(a)>e0f(0)=f(0),
∴f(a)>
f(0)ea
.
故选D.